THE   METALLURGY   OF  IRON  AND   STEEL 


Published   by  the 

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THE  METALLURGY  OF 

IRON  AND  STEEL 


A* 


BY 
BRADLEY   STOUGHTON,  Pn.B.,   B.S. 


FIRST  EDITION  —  FIFTH  IMPRESSION 

(With  numerous  revisions) 


McGRAW-HILL  BOOK  COMPANY 

239  WEST  39TH  STREET,  NEW  YORK 

6  BOUVERIE   STREET,  LONDON,  E.G. 

1908 


-ft 


COPYRIGHT,  1908,  BY  THE  HILL  PUBLISHING  COMPANY 


ENTERED  AT  STATIONERS'  HALL,  LONDON,  ENGLAND 


TO 
PROFESSOR  HENRY   MARION   HOWE,   A.M.,  LL.H, 

BESSEMER  MEDALLIST,    KNIGHT   OF  THE   ORDER  OF 

ST.    STANISLAS,    ETC.,    ETC., 

PRACTITIONER,     INVESTIGATOR,     AUTHOR,     INTERPRETER, 

EDUCATOR  AND  PHILOSOPHER,  WHOM  THE   WORLD 

OF  SCIENCE   DELIGHTS  TO   HONOR, 

THIS  VOLUME   IS 
AFFECTIONATELY  DEDICATED 


222483 


PREFACE 

THE  purpose  of  this  book  is  to  serve  as  a  text-book,  not  only 
for  college  work,  but  for  civil,  mechanical,  electrical,  metallurgical, 
mining  engineers  and  architects,  and  for  those  engaged  in  work  allied 
to  engineering  or  metallurgy.  America  now  produces  almost  as 
much  iron  and  steel  as  the  rest  of  the  world  together,  although 
less  than  eighteen  years  ago  she  held  second  rank  in  this  industry. 
It  seems  fitting  that  the  record  of  this  progress  should  be  brought 
together  into  one  volume  covering  every  branch  of  the  art  of  ex- 
tracting the  metal  from  its  ores  and  of  altering  its  adaptable  and 
ever-varying  nature  to  serve  the  many  requirements  of  civilized 
life. 

I  take  pleasure  in  acknowledging  here,  with  sincere  thanks 
the  assistance  of  many  who  have  aided  in  the  make-up  of  the 
volume,  and  especially  The  Adams  Co.  (Figs.  204-7),  American 
Electric  Furnace  Co.  (Figs.  303-4),  American  Sheet  &  Tinplate  Co. 
(Figs.  9,  11,  23,  and  79),  Bethlehem  Steel  Co.  (Figs.  128-9),  Brown 
Specialty  Machinery  Co.  (Fig.  218),  Connersville  Blower  Co.  (Figs. 
230-1),  Crocker- Wheeler  Co.  (Figs.  155-6,  167),  Francis  G.  Hall 
Esq.  (Figs.  188-91,  196),  Holland  Linseed  Oil  Co.  (Figs.  197- 
200),  Chas.  W.  Hunt,  Esq.,  Secretary,  American  Society  of  Civil 
Engineers  (Fig.  284),  Professor  James  F.  Kemp  (Fig.  8),  Mack- 
intosh, Hemphill  &  Co.  (Figs.  136-7,  150,  152),  Morgan  Construc- 
tion Co.  (Figs.  Ill,  175,  179,  180),  National  Tube  Co.  (Fig.  171), 
S.  Obermayer  Co.  (Figs.  194-5,  201,  203,  223-5,  270),  J.  W. 
Paxson  Co.  (Figs.  226-8),  Henry  E.  Pridmore  (Figs.  208-12), 
John  A.  Rathbone  (Figs.  213-6,  219-20),  each  of  whom  have  kindly 
loaned  electrotypes.  And  of  Dr.  H.  C.  Boynton  (for  Fig.  289),  the 
Brown  Hoisting  Machinery  Co.  (Fig.  14),  Buffalo  Furnace  Works 
(Fig.  266),  H.  H.  Campbell,  Esq.  (Figs.  115-6),  Professor  William 
Campbell  (Fig.  290  and  those  on  page  186),  Carnegie  Steel  Co. 
(Figs.  1 , 80, 160, 163-4, 172, 177) ,  W.  M.  Carr,  Esq.  (Fig.  108) ,  Central 
Iron  &  Steel  Co.  (Figs.  44,  46-7,  49,  51),  Crucible  Steel  Company 


Vi  PREFACE 

of  America  (Fig.  59),  Fiske  &  Robinson  (Fig.  27),  The  Foundry 
(Fig.  117-8,  202),  Harbison-Walker  Refractories  Co.  (Figs.  100, 
181,  229),  Joseph  Hartshorne,  Esq.  (Figs.  41,  43,  45,  48,  50),  Pro- 
fessor Henry  M.  Howe  (Figs.  18,  21,  36-7,  60,  67-70,  120-2,  125-6, 
254,  283),  Lackawanna  Steel  Co.  (Figs.  13,  20,  65,  73-4),  Marion 
Steam  Shovel  Co.  (Fig.  10),  Mesta  Machine  Co.  (Figs.  17,  138, 
143-4,  153,  187),  Morgan  Engineering  Co.  (Figs.  127,  147,  159), 
Professor  A.  H.  Sexton  (Fig.  56),  Wm.  Swindell  &  Bros.  (Figs. 
113-4),  United  Coke  &  Gas  Co.  (Figs.  2-6),  United  Engineering  & 
Foundry  Co.  (Figs.  78,  81,  135,  141,  146,  148-9,  154,  170,  264), 
Wellman-Seaver-Morgan  Co.  (Figs.  92-3, 102-4, 107, 112),  Whiting 
Foundry  Equipment  Co.  (Figs.  271-3).  And  of  O.  S.  Doolittle, 
Esq.,  for  information  upon  the  paint  given  on  page  433,  Frank  E. 
Hall,  Esq.,  for  the  analyses  in  Table  XVIII,  and  W.  J.  Keep,  Esq., 
for  the  figures  in  Table  XXVI. 

But  especially  I  am  indebted  to  the  following  gentlemen,  each 
of  whom  has  read  a  section  of  the  book  and  made  suggestions  for 
its  revision  which  have  been  very  valuable  to  me:  Messrs.  W. 
Arthur  Bostwick,  Stanley  G.  Flagg,  Jr.,  Alfred  E.  Hammer,  Joseph 
Hartshorne,  J.  E.  Johnson,  Jr.,  Carleton  S.  Koch,  Frank  N.  Speller, 
Herbert  L.  Sutton,  and  Hugh  P.  Tiemann. 

BRADLEY  STOUGHTON. 
January  20,  1908. 


TABLE   OF  CONTENTS 


CHAPTER  I.     INTRODUCTION — IRON  AND  CARBON      .       .       .       . 

Definitions,  6.  General  text-books,  reference  books  and 
periodicals  on  the  metallurgy  of  iron  and  steel,  8. 

CHAPTER  II.     THE  MANUFACTURE  OF  PIG  IRON       .... 

Blast-furnace  fuels  and  fluxes,  11.  Varieties  and  distribu- 
tion of  iron  ores,  14.  United  States  deposits  and  transpor- 
tation, 16.  Handling  raw  material  at  a  modern  furnace,  22. 
The  blast  furnace  and  accessories,  24.  Smelting  practice  and 
products,  30.  Calculating  a  blast-furnace  charge,  46. 

CHAPTER  III.     THE  PURIFICATION  OF  PIG  IRON      ... 

Comparison  of  purification  processes.  59.  Distinguishing 
between  the  different  products,  66.  Miscellaneous  purifica- 
tion processes,  67.  General  reference  books  on  steel,  72. 

CHAPTER  IV.     THE  MANUFACTURE  OF  WROUGHT  IRON  AND  CRUCI- 
BLE STEEL  ...        .        .        .        ... 

The  manufacture  of  wrought  iron,  74.  The  carburization 
of  wrought  iron,  85.  References  on  the  manufacture  of 
iron,  93. 


CHAPTER  V.     THE  BESSEMER  PROCESS       . 

References  on  the  Bessemer  process,  125. 

CHAPTER  VI.     THE  OPEN-HEARTH  OR  SIEMENS-MARTIN  PROCESS 

Open-hearth  plant,  127.  Open-hearth  furnace,  132.  Basic 
open-hearth  practice,  145.  Acid  open-hearth  practice,  153. 
Special  open-hearth  processes,  155.  Open-hearth  fuels,  160. 

CHAPTER  VII.     DEFECTS  IN  INGOTS  AND  OTHER  CASTINGS    . 
References  on  defects  in  ingots,  183. 

CHAPTER  VIII.     THE  MECHANICAL  TREATMENT  OF  STEEL 

The  forging  of  metals,  187.  The  reduction  of  metals  in 
rolls,  193.  Parts  of  rolling  mills,  200.  Rolling-mill  practice, 
215.  Wire  drawing,  224.  Pressing,  227.  Comparison  of 
mechanical  methods,  229.  Heating  furnaces,  229.  Refer- 
ences on  mechanical  treatment,  235. 

CHAPTER  IX.     IRON  AND  STEEL  FOUNDING       .       . 

The  making  of  molds,  237.  Design  of  patterns,  260.  Cupola 
melting  of  iron  for  castings,  262.  Comparative  cupola  prac- 
tice, 279.  Other  melting  furnaces,  284.  Melting  steel  for 
castings,  286.  References  on  foundry  practice,  291. 

vii 


PAGES 

3-10 


11-50 


51-73 

74-94 

95-126 
127-172 

173-184 
185-235 


236-291 


Vlll 


TABLE  OF  CONTENTS 


PAGES 

CHAPTER  X.     THE  SOLUTION  THEORY  OF  IRON  AND  STEEL  .        .     292-315 

The  freezing  of  alloys  of  lead  and  tin,  295.  The  freezing  of 
iron  and  steel,  304.  The  solid  solution  of  iron  and  carbon,  308. 
The  complete  Roberts- Austen,  Roozeboom  diagram,  312.  Ref- 
erences, 315. 

CHAPTER  XI.     THE  CONSTITUTION  OF  STEEL 316-332 

The  micro-constituents  of  steel,  316.  The  strength  of  steel, 
324.  Hardness  and  brittleness  of  steel,  328.  Electric  con- 
ductivity of  steel,  329.  Magnetic  properties  of  steel,  330.  Ref- 
erences on  the  constitution  of  steel,  332. 

CHAPTER  XII.     THE  CONSTITUTION  OF  CAST  IRON  ....     333-355 

The  effect  of  carbon  on  cast  iron,  337.  The  effect  of  silicon, 
sulphur,  phosphorus,  and  manganese  on  pig  iron,  341.  The 
properties  of  cast  iron,  345.  References  on  the  constitution 
of  cast  iron,  355. 

CHAPTER  XIII.     MALLEABLE  CAST  IRON 356-369 

References  on  malleable  cast  iron,  369. 

CHAPTER  XIV.     THE  HEAT  TREATMENT  OF  STEEL  .       .       .       .     370-395 

Improper  heating  of  steel,  370.  Hardening  of  steel,  382. 
The  constituents  of  hardened  and  tempered  steels,  389.  Ref- 
erences on  the  heat  treatment  of  steel,  395. 

CHAPTER  XV.     ALLOY  STEELS      .        .        .       .  .     .       .       ,       .     396-421 

Nickel  steels,  398.  Manganese  steel,  405.  Chrome  steel, 
407.  Self-hardening  and  high-speed  tool  steels,  408.  Silicon 
steels,  413.  Vanadium  steels,  414.  Titanium  steels,  419. 
References  on  alloy  steels,  419. 

CHAPTER  XVI.     THE  CORROSION  OF  IRON  AND  STEEL   .       .       .     422-436 

The  cause  and  operation  of  corrosion,  422.  Preservative 
coatings  for  iron  and  steel,  429.  References  on  corrosion,  436. 

CHAPTER  XVII.     THE  ELECTRO-METALLURGY  OF  IRON  AND  STEEL    437-447 

Electro-thermic  ore  smelting,  438.  Electro-thermic  manu- 
facture of  steel,  442.  Electrolytic  refining  of  iron,  446.  Ref- 
erences on  the  electro-metallurgy  of  iron  and  steel,  447. 

CHAPTER  XVIII.     THE  METALLOGRAPHY  OF  IRON  AND  STEEL       .     448-457 

Preparation  of  samples  for  microscopic  examination,  449. 
Developing  the  structure  for  examination,  452.  Microscope 
and  accessories,  454.  Magroscopic  metallography,  454.  Ref- 
erences on  the  metallography  of  iron  and  steel,  457. 

CHAPTER    XIX.     CHEMISTRY    AND    PHYSICS    INTRODUCTORY    TO 

METALLURGY      .       .       .       .        .       .        .       .     ^    .    .     458-488 

Oxygen,  462.  Thermo-chemistry,  464.  Chemical  equations, 
466.  Hydrogen,  469.  Elements,  compounds,  and  radicals, 
471.  Chemical  reactions  and  compounds,  475.  Chemical 
solutions,  480.  Some  principles  of  physics,  482.  Physical 
.properties  of  metals,  484. 


THE   METALLURGY  OF  IRON  AND   STEEL 


/•*.:  :'*:?ie.'4**-^ifeo£.ikAST  FURNACE  AND  STOVES. 


•i    r1 

V 


INTRODUCTION— IRON   AND   CARBON 

This  chapter  is  written  for  those  students  of  iron  and  steel, — whether 
they  be  students  engaged  at  some  university,  or  in  an  engineering 
or  metallurgical  profession, — who  have  previously  completed  a  course 
in  chemistry  and  physics.  For  the  benefit  of  those  who  have  not 
had  a  technical  education,  Chapter  XIX  has  been  especially  pre- 
pared, and  it  is  hoped  that,  if  they  will  read  that  chapter  before  be- 
ginning elsewhere  in  the  book,  all  the  subjects  discussed  in  these 
pages  will  be  readily  intelligible  to  them. 

The  Ferrous  Metals.  —  Iron  and  steel  together  form  the  largest 
manufactured  product  in  the  world,  and  each  of  them  enters 
into  every  branch  of  industry  and  is  a  necessary  factor  in  every 
phase  of  our  modern  civilization.  Cast  iron,  because  of  the  ease 
with  which  it  can  be  melted,  is  produced  in  final  form  in  almost 
every  city  in  the  United  States,  and  only  slightly  less  widely  in 
other  civilized  countries.  The  manufacture  of  steel  is  more 
centralized,  for  economical  reasons,  but  is  several  times  as  great 
as  cast  iron  in  volume.  Wrought  iron  is  lesser  in  amount  than 
either  of  the  others,  but  has  its  own  importance  and  uses.  These 
three  products, — cast  iron,  steel,  and  wrought  iron, — together 
comprise  the  whole  of  the  so-called  "  ferrous  group  of  metals" — that 
is,  the  group  which  we  classify  together  under  the  name  of  "iron 
and  steel."  They  have  two  characteristics  in  common:  First, 
that  iron  is  present  in  all  to  the  extent  of  at  least  92  per  cent.; 
and  second,  that  carbon  is  their  next  most  important  ingredient, 
and  regulates  and  controls  their  chief  qualities.  Their  manufac- 
ture represents  nearly  15  per  cent,  of  all  the  world's  manufacturing 
wealth,  and  is  far  greater  than  any  other  like  industry.  (See 
Table  I.) 

Cast  Iron.  —  Cast  iron  is  impure,  weak,  and  must  be  brought 
to  its  desired  size  and  form  by  melting  and  casting  in  a  mold.  A 

3 


4C,  i,\^  t^THB;MEp^LLtf$GY  OF   IRON  AND   STEEL 

typical  example  would  contain  about  94  per  cent,  iron,  4  per  cent, 
carbon,  and  2  per  cent,  of  other  ingredients  or  impurities. 

Pig  iron  is  a  raw  form  of  cast  iron,  and  malleable  cast  iron  is 
a  semipurified  form. 

Steel.  —  Steel  is  purer  than  cast  iron,  much  stronger,  and  may 
be  produced  in  the  desired  size  and  form  either  by  melting  and 
casting  in  a  mold  or  by  forging  at  a  red  heat.  It  usually  contains 
about  98  per  cent,  or  more  of  iron,  and,  in  different  samples, 
from  1.50  per  cent,  down  to  almost  no  carbon,  together  with  small 
amounts  of  other  ingredients  or  impurities. 

Wrought  Iron.  —  Wrought  iron  is  almost  the  same  as  the 
very  low-carbon  steels,  except  that  it  is  never  produced  by  melting 
and  casting  in  a  mold,  but  is  always  forged  to  the  desired  size 
and  form.  It  usually  contains  less  than  0.12  per  cent,  of  carbon. 
Its  chief  distinction  from  the  low-carbon  steels  is  that  it  is  made 
by  a  process  which  finishes  it  in  a  pasty,  instead  of  in  a  liquid  form, 
and  leaves  about  1  or  2  per  cent,  of  slag  mechanically  disseminated 
through  it. 

Iron.  —  Iron  as  such, — by  which  I  mean  pure  iron,— does  not 
exist  as  an  article  of  commerce,  but  appears  in  service  and  in  the 
market  only  in  the  form  of  cast  iron,  steel  or  wrought  iron, — that  is, 
when  contaminated  with  carbon  and  other  impurities.  Some 
of  these  impurities  are  present  because  they  cannot  cheaply  be 
gotten  rid  of,  and  others,  because,  like  carbon  for  example,  they 
benefit  the  metal  by  giving  it  strength  or  some  other  desirable 
property.  Pure  iron  is  a  white  metal  and  one  of  the  chemical 
elements.  It  is  with  one  exception  the  commonest  and  most 
abundant  metal  in  the  earth,  and  almost  all  rocks  contain  it  in 
greater  or  less  degree,  from  which  we  extract  it  if  it  is  large  enough 
in  amount  to  pay  for  working.  It  practically  never  occurs  in 
nature  in  the  form  of  a  metal,  but  is  always  united  with  oxygen 
to  form  either  a  blackish,  brownish,  reddish  or  yellowish  substance. 
Indeed,  if  it  should  occur  in  metallic  form  it  would  very  soon  be- 
come oxidized  by  the  action  of  air  and  moisture. 

It  is  the  abundance  of  iron  in  the  earth  which  is  the  chief 
cause  of  its  cheapness,  and  therefore  one  reason  why  it  is  used 
more  than  any  other  manufactured  material.  The  other  reason 
is  the  ease  with  which  we  can  confer  upon  it  at  will  some  of  the 
qualities  most  useful  to  man,  of  which  the  most  valuable  is  prob- 
ably its  unequaled  strength,  and  the  most  wonderful  its  magnet- 


INTRODUCTION— IRON   AND   CARBON 


II 


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6  THE  METALLURGY  OF   IRON  AND  STEEL 

ism,  in  which  it  is  not  even  approached  by  any  other  substance. 
What  these  two  properties  alone  mean  in  modern  structural  and 
electrical  engineering  can  scarcely  be  estimated. 

Carbon.  —  Carbon  is  also  a  chemical  element  and  familiar 
to  everyone;  graphite,  lamp-black,  charcoal,  and  diamond  are 
the  various  allotropic  forms  in  which  it  appears.  It  is  a  common 
substance  and  present  in  every  form  of  organic  matter,  while  its 
oxides,  —  carbon  monoxide,  CO;  and  carbon  dioxide,  C02  —  are 
well  known  gases.  Its  chemical  affinity  for  iron  is  very  great; 
iron  practically  always  contains  some  amount,  and,  if  it  is  de- 
sired to  remove  it  entirely,  the  last  traces  are  eliminated  only  with 
extreme  difficulty. 

Iron  and  Carbon.  —  Carbon  has  the  peculiarity  of  conferring 
on  iron  great  strength,  which,  strange  to  say,  it  does  not  itself 
possess,  and  also  hardness,  which  it  possesses  only  in  its  diamond 
allotropic  form.  At  the  same  time  it  takes  away  from  the  iron 
a  part  of  its  ductility,  malleability,  magnetism  and  electric  con- 
ductivity. So  important  is  the  influence  of  carbon  in  regulating 
and  controlling  the  characteristics  of  the  ferrous  metals,  that  they 
are  individually  and  collectively  classified  according  to  the  amount 
and  condition  of  the  carbon  in  them.  The  potent  effect  of  carbon 
must  be  constantly  borne  in  mind  when  we  come  to  describe  the 
manufacture  of  iron  and  steel  and  to  discuss  the  methods  of 
regulating  the  carbon. 

DEFINITIONS 

The  following  definitions  are  selected  from  the  report  of  March 
31,  1906,  of  the  Committee  on  the  Uniform  Nomenclature  of  Iron 
and  Steel  of  the  International  Association  for  Testing  Materials, 
with  slight  changes : 

Cast  Iron.  —  Generically,  iron  containing  so  much  carbon  or 
its  equivalent  that  it  is  not  malleable  at  any  temperature.  Spe- 
cifically, cast  iron  in  the  form  of  castings  other  than  pigs,  or 
remelted  cast  iron  suitable  for  casting  into  such  castings,  as  dis- 
tinguished from  pig  iron,  i.  e.,  cast  iron  in  pigs. 

The  committee  recommends  drawing  the  line  between  cast 
iron  and  steel  at  2.20  per  cent,  carbon  for  the  reason  that  this 
appears  from  the  results  of  Carpenter  and  Keeling  to  be  the 
critical  percentage  of  carbon  corresponding  to  the  point  "a"  in 
the  diagrams  of  Roberts-Austen  and  Roozeboom.  (See  page  314.) 


INTRODUCTION— IRON  AND  CARBON  7 

Pig  Iron.  —  Cast  iron  which  has  been  cast  into  pigs  direct 
from  the  blast  furnace.  This  name  is  also  applied  to  molten 
cast  iron  which  is  about  to  be  so  cast  into  pigs,  or  is  in  a  condition 
in  which  it  could  readily  be  cast  into  pigs  before  it  has  ever  been 
cast  into  any  other  form. 

Gray  Pig  Iron  and  Gray  Cast  Iron.  —  Pig  iron  and  cast  iron 
in  the  fracture  of  which  the  iron  itself  is  nearly  or  quite  concealed 
by  graphite,  so  that  the  fracture  has  the  gray  color  of  graphite. 

White  Pig  Iron  and  White  Cast  Iron.  —  Pig  iron  and  cast  iron 
in  the  fracture  of  which  little  or  no  graphite  is  visible,  so  that 
their,  fracture  is  silvery  and  white. 

Mottled  Pig  Iron  and  Mottled  Cast  Iron.  —  Pig  iron  and  cast 
iron,  the  structure  of  which  is  mottled,  with  white  parts  in  which 
no  graphite  is  seen,  and  gray  parts  in  which  graphite  is  seen. 

Malleable  Cast  Iron.  —  Iron  which  when  first  made  is  cast  in 
the  condition  of  cast  iron,  and  is  made  malleable  by  subsequent 
treatment  without  fusion. 

Malleable  Iron.  —  The  same  as  wrought  iron.  A  name  used 
in  Great  Britain,  but  not  in  the  United  States,  except  carelessly 
as  meaning  "Malleable  cast  iron." 

Steel.  —  Iron  which  is  malleable  at  least  in  some  one  range 
of  temperature,  and  in  addition  is  either  (a)  cast  into  an  initially 
malleable  mass;  or  (6)  is  capable  of  hardening  greatly  by  sudden 
cooling;  or  (c)  is  both  so  cast  and  so  capable  of  hardening. 

Wrought  Iron.  —  Slag-bearing,  malleable  iron,  which  does  not 
harden  materially  when  suddenly  cooled. 

In  the  definition  of  steel  the  first  sentence  ("is  malleable  at 
least  in  some  one  range  of  temperature")  distinguishes  steel 
from  cast  iron  and  pig  iron;  the  second  sentence  ("is  cast  into  an 
initially  malleable  mass")  distinguishes  it  from  malleable  cast 
iron,  and  the  third  sentence  ("is  capable  of  hardening  greatly  by 
sudden  cooling")  distinguishes  it  from  wrought  iron.  At  the 
best,  however,  the  definition  of  steel  is  in  a  shockingly  bad  con- 
dition, and  has  been  brought  to  it  by  a  series  of  events  which  shows 
the  carelessness  of  the  buying  public  and  the  greed  of  men  who 
will  appropriate  the  name  for  their  product  that  will  bring  them 
the  best  price  without  regard  to  whether  the  name  really  fits  or 
not.1 

1  See  page  173  of  reference  No.  1,  at  the  end  of  this  chapter,  and  page  6 
of  No.  2. 


8  THE   METALLURGY  OF   IRON  AND   STEEL 

GENERAL  TEXT-BOOKS,  REFERENCE  BOOKS  AND  PERIODICALS  ON 
THE  METALLURGY  OF  IRON  AND  STEEL 

(For  further  references,  see  the  end  of  Chapter  III.} 

1.  Prof.  H.  M.  Howe.     "Iron,  Steel,  and  Other  Alloys,"  1903. 

Published  by  Sauveur  &  Whiting,  Boston,  Mass.  This 
book  contains  three  chapters  upon  the  "Manufacture  of 
Iron  and  Steel "  and  ten  chapters  upon  its  constitution  and 
properties,  especially  from  the  standpoint  of  metallography. 
Upon  this  latter  subject  it  is  without  an  equal  and,  like 
the  same  author's  larger  work,  bids  fair  to  remain  the 
standard  authority  for  many  years  to  come. 

2.  H.    H.    Campbell.     "The    Manufacture    and    Properties    of 

Iron  and  Steel."  Fourth  edition.  New  York  and  London. 
1907.  This  is  a  great  reference  book  by  one  of  the  best 
of  the  practical  American  metallurgical  engineers.  It  is 
undoubtedly  the  best  reference  book  upon  the  manufacture 
of  iron  and  steel,  but  is  not  intended  especially  for  beginners 
or  those  without  technical  education. 

3.  James  M.  Swank.     "  Directory  to  the  Iron  and  Steel  Works 

of  the  United  States."  Embracing  the  Blast  Furnaces, 
Rolling  Mills,  Steel  Works,  Forges,  and  Bloomaries  in 
Every  State  and  Territory.  Prepared  and  published  by 
The  American  Iron  and  Steel  Association.  Philadelphia. 
The  first  edition  of  this  book  appeared  in  1873,  and  the 
seventeenth  edition  in  1907.  The  data  given  are  very  com- 
plete and  are  classified  for  convenient  reference. 

4.  James  M.  Swank.     "  History  of  the  Manufacture  of  Iron  in 

All  Ages,  and  Particularly  in  the  United  States  from  1585 
to  1892."  Philadelphia. 

5.  "Ryland's  Colliery,-  Iron,  Steel,  Tin-Plate,  Engineering  and 

Allied  Trades'  Directory  (For  Great  Britain  only)  with 
Brands  and  Trade  Marks."  1906.  Published  by  Eagland 
&  Co.,  Ltd.,  London. 

6.  Andrew  Alexander  Blair.     "The  Chemical  Analysis  of  Iron." 

A  Complete  Account  of  all  the  best  known  Methods  for  the 
Analysis  of  Iron,  Steel,  Pig  Iron,  Iron  Ore,  Limestone, 
Slag,  Clay,  Sard,  Coal,  Coke,  ard  Furnace  and  Producer- 
Gases.  Sixth  edition.  Philadelphia  and  London.  1906. 


INTRODUCTION— IRON  AND   CARBON  9 

7.  J.  0.  Arnold.     "Steel  Works  Analysis."     London  and  New 

York.     1895. 

8.  The   Journal  of  the   Iron  and  Steel  Institute.     Published  in 

London.  Vol.  i,  1869;  vol.  Ixxiii,  1907.  This  periodical 
appears  twice  a  year  and  contains  not  only  many  original 
articles  of  very  great  value  but  also  an  almost  complete 
collection  of  abstracts  of  the  literature  of  iron  and  steel 
that  is  published  anywhere,  classified  under  headings  for 
convenient  reference.  Anyone  beginning  the  study  of  any 
branch  of  iron  and  steel  metallurgy  should  commence  with 
this  journal^  as  soon  as  the  text-books  have  been  con- 
sulted. 

9.  Stahl  und  Eisen.     Published  in  Duesseldorf.     Vol.  i,  1881; 

vol.  xxvii,  1907.  This  is  the  best  German  periodical  on 
iron  and  steel,  and  contains  not  only  many  valuable  original 
articles  and  abstracts  but  also  translations.  I  have  found 
it  particularly  useful  in  this  latter  connection,  because  of 
its  translations  of  many  articles  from  the  Swedish. 

10.  Revue  de   Metallurgie.      Published  in   Paris.      Vol.   i,    1904; 

vol.  iv,  1907.  This  is  a  very  valuable  periodical  for  those 
who  read  French,  not  only  for  its  original  articles  but  also 
for  its  abstracts.  Upon  the  more  scientific  side  of  metal- 
lurgy, that  is  to  say  the  properties  and  constitution  of 
iron  and  steel,  alloy  steels,  etc.,  it  is  without  an  equal. 

11.  The  Mineral  Industry.     Its   statistics,   technical   and  trade. 

Published  in  New  York.  Vol.  i,  1892;  vol.  xvi,  1907.  This 
contains  a  review  every  year  of  the  technology  and  trade 
of  each  of  the  metals  listed  alphabetically,  as  well  as  the 
statistics  of  production,  price,  etc.  The  articles  usually 
include  a  review  of  the  progress  of  the  metallurgy  during 
the  year. 

12.  The  Iron  Age.      Published    in    New    York.      Vol.    i,    1869; 

vol.  Ixxix,  1907.  This  is  the  oldest  and  largest  of  the 
American  iron  and  steel  technical  magazines,  and  deals  not 
only  with  the  scientific  and  technical  side  of  the  subject, 
but  also  acts  as  a  sort  of  a  weekly  newspaper  upon  the  con- 
dition of  the  iron  trade  and  recent  happenings  of  interest. 

13.  Transactions  of  the  American  Institute  of  Mining  Engineers. 

Published  in  New  York.  Vol.  i,  1871;  vol.  xxxviii,  1907. 
The  American  Institute  of  Mining  Engineers  is  the  leading 


10  THE   METALLURGY   OF   IRON   AND   STEEL 

aggregation  of  both  mining  engineers  and  metallurgists  in 
America.  These  transactions  contain  many  original  articles 
of  value. 

14.  James  M.  Swank.     Annual  Statistical  Report  of  the  Secretary 

of  the  American  Iron  and  Steel  Association,  containing 
detailed  statistics  of  the  American  and  foreign  iron  trade. 
Published  in  Philadelphia. 

15.  Iron  Trade  Review.     Published  in  Cleveland,  Ohio.    Although 

this  magazine  aims  to  deal  principally  with  iron  trade 
conditions,  it  contains  also  a  great  many  technical  articles 
of  importance. 

16.  Metallurgie.     Published  in  Halle  am  See.     Vol.  i,  1904;  vol. 

iv,  1907.  This  German  magazine  contains  a  great  many 
original  articles  and  abstracts. 

17.  Annales  des  Mines.    Published  in  Paris.    Vol.  i,  1816.    Tenth 

series.     Vol.  xi,  1907. 

18.  Revue  Universelle  des  Mines,  de  la  Metallurgie  des  Travaux 

Publics,  des  Sciences  et  des  Arts  Appliques  a  r Industrie. 
Vol.  i,  1857;  Fourth  series,  vol.  xvii,  1907. 

19.  Osterreichische  Zeitschrift  fur  Berg-  und  Huttenwesen.     Pub- 

lished in  Vienna.     Vol.  i,  1853;  vol.  Iv,  1907. 


II 

THE  MANUFACTURE  OF   PIG   IRON 

WHATEVER  material  we  are  to  manufacture  —  cast  iron, 
wrought  iron,  or  steel  —  or  for  whatever  purpose  the  metal  is  to 
be  used,  the  first  step  in  the  operation  is  smelting  iron  ore  in  a 
blast  furnace  with  fuel  and  flux,  and  obtaining  cast  iron  or  pig 
iron,  terms  used  synonymously  in  the  United  States.1  The  pig 
iron  thus  produced  is  an  impure  grade  of  iron,  containing  usually  3 
to  4  per  cent,  of  carbon,  up  to  4  per  cent,  of  silicon,  up  to  1  per  cent, 
of  manganese,  and  a  few  hundredths  of  1  per  cent,  each  of  sulphur 
and  phosphorus.2  The  amount  of  pig  iron  made  exceeds  that  of 
any  other  product  manufactured  by  man. 

BLAST-FURNACE  FUELS  AND  FLUXES 

Fuels  are  impure  forms  of  carbon.  By  their  union  with  oxygen 
they  furnish  heat: 

C  +  O   =CO    (generates  29,160  calories).3 
CO  +  O  =COa  (       "  68,040        "     ). 

C+O2=CO2(      "  97,200        "     ). 

The  temperatures  necessary  for  smelting  are  obtained  in  this 
way.  They  also  act  as  the  chemical  agents  to  separate  the  iron 
from  the  oxygen  with  which  it  is  combined  in  ores: 

Fe2O3+3  C  =3  CO+2  Fe  (absorbs  108,120  calories).3 
Fe3O4+4C=4CO+3Fe  (      "        154,160        "     ). 

The  carbon  contained  in  the  pig  iron  is  also  dissolved  from  the 
fuel,  directly  or  indirectly. 

1More  strictly  speaking,  'pig  iron'  applies  to  the  virgin  product  of  the 
blast  furnace,  and  '  cast  iron '  designates  pig  iron  that  has  been  cast  into 
molds  of  some  final  and  useful  shape,  usually  after  a  remelting. 

2  In  foundry  and  basic  pig  irons,  the  impurities  are  higher  than  this. 

3  All  heat  effects  of  chemical  reactions  are  given  in  calories  per  molecular 
weight  in  grams  throughout  the  book. 

11 


12  THE   METALLURGY   OF    IRON   AND   STEEL 

Charcoal.  —  The  purer  the  carbon  the  better  it  serves  the  pur- 
poses mentioned.  For  this  reason  charcoal,  which  has  the  least 
amount  of  objectionable  impurities,  was  once  the  great  metallurgi- 
cal fuel.  Even  to-day  blast  furnaces  use  charcoal  for  the  produc- 
tion of  pure  pig  relatively  free  from  sulphur.  Except  in  favored 
localities,  charcoal  is  costly.  Furthermore,  its  weakness  permits 
it  .to  crush  easily;  so  charcoal  furnaces  are  restricted  to  small  sizes, 
and  'charcoal  iron'  is  higher  in  price. 

Anthracite.  —  Anthracite  is  purer  than  coke,  but  its  denseness 
makes  it  offer  a  large  resistance  to  the  blast  in  furnaces  having 
much  height. 

Coke.  —  Coke  is  the  great  blast-furnace  fuel,  and  a  near-by 
supply  of  this  material  makes  Pittsburg,  Chicago,  Alabama,  and 
Colorado  the  great  smelting  centers  that  they  are.  In  the  United 


—  STANDARD  AMERICAN  BEEHIVE  OVEN. 

Charge,  5  net  tons  coal.  Coking  time,  72  hours.  The  gases 
distilled  from  the  coal  burn  in  the  dome  of  the  oven  and  thus  heat 
the  coal  to  produce  more  distillation. 


States  practically  94  per  cent,  of  the  pig  iron  is  made  with  coke 
as  fuel,  5  per  cent,  with  anthracite  as  fuel,  and  1  per  cent,  with 
charcoal. 

A  bituminous  coking  coaK  contains  about  30  per  cent,  by 
weight  of  volatile  matter.  When  this  coal  is  heated,  or  '  coked/ 
the  volatile  matter  is  driven  off,  leaving  a  porous,  spongy  mass  of 
a  silvery  gray  color  and  good  strength.  This  is  coke,  and  an 


THE  MANUFACTURE   OF   PIG   IRON 


13 


analysis  of  a  specimen  from  the  famous  Connellsville  region  near 
Pittsburg  is:  Volatile  matter  =0.67  per  cent.;  fixed  carbon  =87.05 
percent.;  ash  =  10. 60  per  cent.;  sulphur  =0.74  per  cent.;  phos- 
phorus =  0.016  per  cent. 

Fluxes.  —  The  ash  of  fuels  will  not  melt  readily.  By  adding 
the  correct  amount  of  lime  to  them  they  are  transformed  into  a 
fusible  mass,  which  remains  in  a  liquid  form  in  the  furnace  and  is 
easily  removed  by  opening  a  hole  in  the  side.  This  fusible  ma- 


FIG.  3.  —  50  OTTO-HOFFMANN  BY-PRODUCT,  OR  RETORT,  COKE  OVENS. 


terial  is  known  as  slag  or  cinder,  and  the  added  lime  is  known  as 
flux.  The  flux  is  usually  added  in  the  form  of  limestone  (CaCO3), 
but  the  heat  in  the  upper  layers  of  the  furnace  drives  off  the  car- 
bonic acid,  leaving  lime  (CaO). 

The  gangue  of  our  iron  ores  consists  usually  of  silica,  alumina, 
etc.,  and,  like  the  fuel  ash,  requires  the  addition  of  the  correct 
amount  of  limestone  flux  to  make  it  into  a  fusible  slag.  In  the 
Pittsburg  district  we  charge  about  1200  Ib.  of  limestone,  2200  Ib. 
of  coke,  and  4000  Ib.  of  ore  for  every  long  ton  of  pig  iron  made. 
The  amount  of  each  is  increasing,  however,  from  time  to  time,  as 
the  higher-grade  ores  are  becoming  exhausted  and  there  are  more 
impurities  to  be  fluxed  and  melted. 


14 


THE   METALLURGY   OF   IRON   AND   STEEL 


VAKIETIES  AND  DISTRIBUTION  OF  IRON  ORES 

The  iron  ores  used  for  smelting  consist  of  chemical  compounds 
of  iron  and  oxygen  containing  more  or  less  water,  either  in  the 


FIG.  4.  —  HORIZONTAL  SECTION  THROUGH  A  RETORT  OF  A 
BY-PRODUCT   OVEN. 

The  gases  from  the  coal  burn  in  flues  on  the  side  of  the  retort  which  contains  the  coal. 

form  of  moisture  or  chemically  combined  as  water  of  crystalliza- 
tion. 

Hematite  (Fe2O3) .  —  The  best  known  of  these  ores  is  hematite, 
containing  when  pure  70  per  cent,  of  iron.     The  red  or  brown 


FIG.  5.  —  STRUCTURE  OF  BEEHIVE  COKE. 


hematites  are  the  richer  varieties  (Lake  Superior  deposits,  contain- 
ing, in  some  cases,  as  much  as  68  per  cent,  of  iron),  while   the 


THE   MANUFACTURE   OF   PIG   IRON 


15 


hydrated  hematites,  or  limonites,  usually  contain  a  good  deal  of 
water  of  crystallization  and  are  consequently  poorer  in  iron,  not 
often  yielding  much  more  than  50  per  cent.  iron. 

Oolitic  hematite  is  a  variety  that  exists  in  the  form  of  spherical 
grains  or  nodules.  It  is  important  because  it  sometimes  contains 
limestone  and  is,  therefore,  valuable  not 
only  for  the  iron  but  for  the  fluxing  quality 
of  the  lime.  The  Minette  ore  of  Lothringen 
(formerly  Lorraine),  Luxemburg,  and  France 
is  an  enormous  deposit  of  this  oolitic  hema- 
tite, running  from  30  to  35  per  cent,  iron  and 
giving  a  pig  iron  containing  about  2  per 
cent,  of  phosphorus.  This  ore  is  the  basis 
of  the  iron  industry  of  Germany,  France, 
and  Belgium,  and,  upon  judicious  mixing  of 
varieties,  when  necessary,  is  self-fluxing. 

Magnetite  (Fe3O4). — Magnetite  contains, 
when  pure,  enough  iron  (72.4  per  cent.)  to 
attract  the  magnet.  In  the  United  States  it 
is  often  mixed  with  other  impurities,  such  as 
silica,  titanium,  and  phosphorus,  so  much  so 
as  to  render  the  ore  either  too  poor  in  iron 
to  be  smelted  profitably,  or  too  high  in  phos- 
phorus to  make  good  steel,  or  so  high  in 
titanium  as  to  interfere  with  the  blast-furnace 
smelting  by  producing  sticky  slags  which  are 
not  easily  handled. 

The  magnetite  ores  of  Sweden  are,  how- 
ever, the  purest  ores  that  exist  in  large 
quantities  anywhere,  and  form  one  of  the 
sources  of  the  Swedish  iron  and  steel,  which 
is  famous  all  over  the  world  for  its  purity, 
that  is,  for  its  freedom  from  the  objection- 
able elements  sulphur  and  phosphorus.  It 
is  these  Swedish  products  which  supply  the  steel  industry  of 
Sheffield  with  pure  material  for  its  tool  steel  and  cutlery. 

Siderite  (FeCOs). — Another  variety  of  iron  ore  is  the  so- 
called  'spathic'  iron  ore,  or  siderite,  which  is,  however,  without 
any  importance  in  the  United  States.  This  forms  the  famous 
*  clay  ironstone '  of  the  Cleveland  district  in  England.  It  is  poor 


FIG.  6.  — CROSS-SEC- 
TION OF  RETORT. 
Structure  of  By-product 
Coke. 


16 


THE   METALLURGY  OF   IRON  AND   STEEL 


in  iron  and  is  therefore  no  longer  smelted  in  any  quantity  in  the 
United  States  in  competition  with  the  rich  hematites.     This  ore  is 


FIG.  7.  —  BATTERIES  OF  BEEHIVE  OVENS. 

almost  always  calcined  before  smelting  to  expel  the  carbonic  acid, 
in  order  to  save  the  blast  furnace  the  extra  work  of  this  expul- 
sion in  its  upper  levels. 


UNITED  STATES  DEPOSITS  AND  TRANSPORTATION 

In  the  United  States  ores  of  iron  are  very  widely  distributed, 
as  will  be  seen  by  reference  to  the  map  on  page  17,  the  black  spots 
on  which  represent  notable  deposits.  The  smelting  of  ore  also 
shows  a  wide  distribution.  Blast  furnaces  are  in  operation  in 
twenty-two  states,  including  Washington,  Minnesota,  New  York, 
and  Massachusetts  on  the  north;  Colorado,  Texas,  and  Alabama  on 
the  west  and  south.  The  great  pig  iron  centers  are:  (1)  The  dis- 
trict that  includes  Western  Pennsylvania  and  Ohio,  which  pro- 
duces more  than  one-half  of  the  pig  iron  of  the  country;  (2)  Illinois, 
and  (3)  Alabama. 

It  is  not  to  be  supposed  that  all  the  deposits  marked  on  the 
map  are  extensively  worked  for  their  iron.  The  rich  hematite 
deposits  of  the  Lake  Superior  district  furnish  annually  about 
40,000,000  tons,  which  yield  more  than  three-quarters  of  the  pig- 
iron  production  of  the  country.  The  only  other  districts  which 
produce  more  than  1,000,000  tons  a  year  are  in  the  states  of  Alabama 
and  New  York.  Most  of  the  other  deposits  are  mined  only  for  local 


THE  MANUFACTURE   OF  PIG   IRON 


17 


treatment.     In  addition,  a  total  of  nearly  1,000,000  tons  of  ore  per 
year  are  imported  from  Cuba,  Spain,  and  other  foreign  countries, 


100    .Longitude  West      90    from  Greenwich        75-^ 

A  N  A 


FIG.  8. —  FROM  KEMP'S  "ORE  DEPOSITS  OF  THE  UNITED  STATES." 

principally  for  smelting  by  blast  furnaces  on  or  near  the  Atlantic 
coast. 

Ore  Transportation.  —  The  peculiarity  of  the  Lake  Superior 
deposits  is  that  almost  none  of  the  ore  is  smelted  locally,  but  is 
transported  a  distance  of  800  miles  or  more  in  order  to  bring  it  to 


FIG.  9.  —  A  LAKE   SUPERIOR  ORE  MINE. 

the  coke.  Thus,  South  Chicago,  Western  Pennsylvania,  and  Ohio 
receive  the  bulk  of  the  ore  shipped  from  the  Lake  Superior  mines. 
Since  the  amount  of  coke  used  in  the  blast  furnaces  is  only  about 
one-half  the  weight  of  the  ore,  it  might  seem  uneconomical  to  carry 


THE   MANUFACTURE   OF   PIG   IRON 


19 


the  latter  to  the  former.  But  coke  is  bulky  in  proportion  to  its 
weight;  furthermore,  it  suffers  a  good  deal  of  waste  in  transporta- 
tion in  consequence  of  its  friability  and  of  the  fact  that  so  much 
of  it  is  broken  down  into  pieces  less  than  an  inch  in  diameter 
(technically  known  as  '  breeze ')  which  is  not  suitable  for  charging 
into  the  blast  furnace.  The  ore,  on  the  other  hand,  may  be  handled 
by  the  cheapest  and  most  rapid  labor-saving  devices.  Indeed,  in 


FIG.   11. —  LOADING  AN  ORE  BOAT. 

many  cases,  the  ore  is  never  touched  by  shovels  in  the  hands  of 
man,  but  is  mined,  charged,  and  discharged  in  units  of  several  tons 
each,  and  often  by  means  of  gravity. 

The  mining  and  transportation  of  this  great  amount  of  ma- 
terial is  in  itself  a  mighty  industry,  every  advance  in  which 
has  contributed  in  no  small  share  to  the  increasing  volume  and 
importance  of  the  iron,  steel,  and  other  industries  of  the  United 
States. 

Mining.  —  Some  of  the  Lake  Superior  deposits  lie  near  the 
surface  and  are  therefore  cheaply  mined.  This  is  especially  true 
of  the  soft,  earthy  deposits  of  the  Mesabi  range,  which  are  some- 
times worked  in  great  open  cuts,  the  ore  being  loaded  upon  cars  by 
mammoth  steam  shovels,  or  sometimes  by  the  caving  method,  the 
ore  falling  by  gravity  into  cars  situated  in  underground  tunnels. 
The  massive,  or  rock,  ores  are  more  costly  to  extract,  and  the 
utmost  skill  of  American  blast-furnace  men  has  been  exercised  to 


20 


THE  METALLURGY   OF   IRON  AND   STEEL 


employ  as  large  a  portion  of  the  earthy  ores  as  possible  without 
choking  up  the  furnace. 

Transportation.  —  On  reaching  the  shore  of  the  lake  the  ore 
train  is  run  out  above  a  long  line  of  ore  bins  supported  on  a  wharf 
extending  over  the  deep  water  of  Lake  Superior.  Alongside  of 
this  wharf  the  ore  boats,  capable  of  taking  a  load  of  10,000  or 
13,000  tons  of  ore,  are  docked.  The  hatches  of  these  great  boats 


FIG.  12.  —  BROWN-HOIST  APPARATUS  UNLOADING  AN  ORE  BOAT. 


are  placed  such  a  distance  apart  that  the  hinged  ore  chutes  of  the 
bins  may  be  swung  down  and,  when  the  gates  are  opened,  the  ore 
allowed  to  flow  directly  into  the  hold  of  the  vessel.  In  a  few 
minutes  the  vessel  has  received  her  full  cargo  and  is  ready  to  start 
on  its  long  journey  down  the  chain  of  inland  lakes. 

Sometimes  in  long  strings  of  three  or  four,  in  tow  together, 
sometimes  singly  or  in  pairs,  the  boats  travel  from  one  end  of  Lake 
Superior  to  the  other  and  come  to  the  great  canal  of  Sault  Ste. 
Marie.  This  canal  deserves  a  passing  mention  because  of  the 
enormous  benefit  which  its  construction  has  conferred  upon  the" 
iron  industry.  It  is  two  miles  long,  and  for  about  three  months  of 
the  year  is  closed  to  navigation  by  the  ice;  nevertheless,  the  total 
tonnage  of  the  cargoes  passing  through  it  annually,  by  far  the 
greater  part  of  which  consists  of  iron  ore,  amounts  to  nearly 
55,000,000,  a  volume  three  times  as  great  as  that  borne  by  the 
next  greatest  canal,  namely,  the  Suez  Canal,  which  forms  the 


THE  MANUFACTURE   OF   PIG   IRON 


21 


great  water  highway  from  Europe  and  the  Mediterranean  to  the 
East. 

After  passing  through  the  one  lock  of  the  'Soo'  canal,  the 
stream  of  ore  divides  into  two  parts.  One  part  turns  to  the  west- 
ward and  supplies  the  great  blast  furnaces  of  Chicago  and  Mil- 
waukee ;  but  much  the  larger  portion  travels  down  Lake  Huron  and 
Lake  St.  Clair  and  is  discharged  at  some  one  of  the  many  great  un- 
loading points  on  the  southern  shore  of  Lake  Erie,  where  it  is  either 
smelted  near  by  or  loaded  on  railroad  cars  for  transportation  to 
Pittsburg,  Youngstown,  or  one  of  the  other  great  blast-furnace 
centers. 

Unloading.  —  The  unloading  of  boats  is  accomplished  with 
almost  as  great  celerity  as  the  loading,  and  by  means  of  mechanical 
unloading  machinery  a  steamer  containing  as  much  as  10,300  tons 


FIG.  13.  —  HULETT  ELECTRIC  UNLOADER. 

of  ore  has  been  completely  discharged  in  4  hours  and  30  minutes. 
Nor  is  any  time  wasted  in  coaling  the  vessel  for  a  second  journey  up 
the  lakes  and  back.  Great  machines  pick  up  whole  railroad  cars 
of  fuel  and  empty  them  bodily  into  the  chute  which  connects  with 
the  bunkers  of  the  vessel,  many  of  the  ore  steamers  being  so  con- 
structed that  this  wholesale  loading  of  coal  can  go  on  at  the  same 
time  that  ore  is  being  discharged. 


22  THE  METALLURGY  OF   IRON  AND   STEEL 

HANDLING  RAW  MATERIAL  AT  A  MODERN  FURNACE 

Behind  the  blast  furnace  are  situated  two  long  rows  of  storage 
bins,  one  of  which  is  shown  in  elevation  in  Fig.  15.  These  bins 
are  filled  by  bottom-dumping  railroad  cars  which  bring  the  ore  to 
the  furnaces,  or  by  mechanical  apparatus  from  the  great  piles  of 
ore  stored  conveniently  near.  Between  and  under  these  two  rows 
of  bins  runs  a  track  on  which  little  trains  of  ore  larries  are  trans- 
ferred back  and  forth,  being  first  filled  with  a  weighed  amount  of 
ore,  limestone,  or  fuel,  and  then  switched  into  a  position  from 
which  they  can  deposit  their  contents  into  the  loading  skip  of  the 
blast  furnace. 

Loading  the  Furnace.  —  The  next  step  in  the  handling  of  the 
raw  material  is  to  bring  the  ore,  together  with  the  necessary  fuel 
and  flux,  into  the  mouth  of  the  huge  furnace  that  is  to  convert  it 
into  pig  iron.  In  one  of  the  big  modern  American  furnaces,  work- 


FIG.   14.  —  ORE-HANDLING  MECHANISM  AT  BLAST  FURNACE. 

ing  at  top  speed,  the  amount  of  material  which  must  be  dumped 
into  the  top  during  24  hours  will  frequently  exceed  2000  tons,  and 
the  charging  must  go  on  for  365  days  a  year  with  never  a  delay  of 
more  than  a  few  hours  at  a  time. 

In  the  modern  type  of  furnace  this  loading  is  accomplished 
altogether  by  mechanism  operated  and  controlled  from  the  ground 
level,  and  no  men  are  required  to  work  at  the  top  of  the  furnace. 
In  Fig.  15  is  a  section  of  such  a  furnace  showing  one  method  of 
loading,  —  a  double,  inclined  skipway  extending  above  the  top  of 
4he  furnace.  One  skip  is  seen  discharging  its  load  of  ore,  or  fuel 


THE   MANUFACTURE   OF   PIG   IRON 


23 


and  flux,  into  the  hopper,  while  the  second  skip  is  at  the  bottom  of 
the  incline  ready  to  be  loaded  with  its  charge. 

Double  Bell  and  Hopper.  —  The  upper  hopper  of  the  furnace  is 
closed  at  the  bottom  by  an  iron  cone,  known  as  a  'bell/     This  bell 


FIG.    15.  —  CROSS-SECTION   OF   BLAST   FURNACE   AND   SKIP   HOIST.     ~ 

is  pressed  up  against  the  bottom  of  the  hopper  by  the  lever  of  the 
counterweight,  as  shown,  but  may  be  lowered  by  operating  the 


24  THE  METALLURGY   OF   IRON  AND   STEEL 

cylinder  Af,  to  allow  the  charge  to  fall  into  the  true  hopper,  /,  of 
the  blast  furnace.  In  this  way  the  true  hopper  of  the  furnace  is 
progressively  filled  with  ore,  flux,  and  fuel.  This  hopper,  /,  is  also 
closed  at  the  bottom  by  a  similar  bell,  A.  The  lowering  of  this 
bell  is  also  controlled  by  mechanism  operated  from  the  ground 
level.  At  intervals  this  operation  is  effected  and  the  contents  of 
the  hopper  allowed  to  fall  in  an  annular  stream,  distributing  itself 
in  a  regular  layer  on  top  of  the  material  already  in  the  furnace  and 
reaching  to  within  a  few  feet  of  the  bottom  of  the  bell.  As  the 
upper  bell,  B,  is  now  held  up  against  the  bottom  of  the  upper 
hopper,  there  is  never  a  direct  opening  from  the  interior  of  the 
blast  furnace  to  the  outer  air,  so  that  the  escape  of  gas,  resulting 
formerly  in  the  long  flame  rising  from  the  top  of  the  blast  furnace 
whenever  material  Was  dropped  into  the  interior,  no  longer  occurs 
at  our  modern  plants. 

This  is  not  the  only  means  of  handling  the  raw  material  for  the 
blast  furnace.  Several  varieties  of  mechanism  are  extensively 
used,  but  the  description  given  heretofore  will  serve  to  illustrate 
the  general  principles  of  labor-saving  mechanisms  in  connection 
with  charging  the  blast  furnace.  It  will  be  seen  that  the  ore  is 
transferred  from  one  receptacle  to  another  by  means  of  gravity 
wherever  possible. 

THE  BLAST  FURNACE  AND  ACCESSORIES 

The  blast  furnace  itself  consists  of  a  tall  cylindrical  stack  lined 
with  an  acid  (silicious)  refractory  fire-brick,  the  general  form  and 
dimensions  being  shown  in  Fig.  15.  The  hearth  or  crucible  is  the 
straight  portion  occupying  the  lower  8  ft.  of  the  furnace.  Above 
that  extends  the  widening  portion,  called  the  bosh,  which  reaches 
to  that  portion  in  the  furnace  having  the  greatest  diameter.  The 
stack  extends  throughout  the  remainder  of  the  furnace,  from  the 
bosh  to  the  throat.  The  brickwork  of  the  hearth  is  cooled  by 
causing  water  to  trickle  over  the  outside  surface. 

Tuyeres.  —  Through  the  lining  of  the  furnace,  just  at  the  top 
of  the  hearth,  extend  the  tuyeres  —  8  to  16  pipes  having  an  in- 
ternal diameter  of  4  to  7  in.,  through  which  hot  blast  is  driven  to 
burn  the  coke  and  furnish  the  heat  for  the  smelting  operation. 
The  '  tuyere  notches/  or  openings  through  which  the  tuyere  pipes 
_  enter,  as  well  as  the  tuyeres  themselves,  are  surrounded  by  hollow 


THE  MANUFACTURE   OF   PIG   IRON 


25 


bronze  rings  set  in  the  brickwork,  through  which  cold  water  is  con- 
stantly flowing  to  protect  them  from  being  melted  off  at  the  inner 
ends.  The  number  and  size  of  the  tuyeres  are  in  proportion  to  the 
diameter  of  the  hearth,  the  volume  and  pressure  of  the  blast,  etc., 
the  blast  being  given  sufficient  velocity  to  carry  it,  distributed  as 
evenly  as  possible,  to  the  very  center  of  the  furnace. 

Discharge  Holes.  —  On  the  side  of  the  furnace,  and  30  to  40  in. 
below  the  level  of  the  tuyeres,  the  'cinder  notch'  or  ' monkey'  is 
situated.  This  is  protected  by  a  water-cooled  casting,  and  the 
hole  is  closed  by  chilling  the  iron  in  it  with  an  iron  plug. 

In  the  front,  or  breast,  at  the  very  bottom  level  of  the  crucible, 
is  the  iron  tap-hole,  from  which  all  the  liquid  contents  of  the 


Eye  Sight 


FIG.  16.  — PARTS  OF  A  BLAST  FURNACE  TUYERE. 

furnace  can  be  completely  drained.     This  is  a  large  hole  in  the 
brickwork,  and  is  closed  with  several  balls  of  clay. 

Bosh.  —  The  hottest  part  of  the  furnace  is  near  the  tuyeres 
and  a  few  feet  above  them.  In  order  to  protect  the  brickwork  of 
the  bosh  from  this  heat,  a  number  of  hollow  wedge-shaped  cast- 
ings are  placed  therein,  through  which  cold  water  circulates.  The 
brickwork  is  furthermore  protected  by  a  deposition  of  a  layer  of 
carbon,  similar  to  lampblack,  on  its  internal  surface,  covered  by  a 
layer  of  a  sort  of  slag,  replacing  part  of  the  brickwork.  This 
deposition  of  carbon  comes  about  through  the  reaction  of  the 


26 


THE   METALLURGY   OF    IRON   AND   STEEL 


furnace  operation  itself,  in  the  following  manner:  For  the  correct 
conduct  of  the  smelting  operation,  and  especially  for  the  carrying 
off  of  the  sulphur  in  the  slag,  it  is  necessary  that  a  very  powerful 
reducing  influence  must  exist;  this  reducing  influence  is  produced 


FIG.  17.  —  A  BATTERY  OF  BLAST  FURNACE  BLOWING  ENGINES. 


THE  MANUFACTURE   OF   PIG   IRON  27 

by  an  excess  of  coke,  and  one  of  its  results  is  the  precipitation  of 
finely  divided  carbon  on  the  internal  walls  of  the  furnace.  It  is 
this  thin  layer  of  slag  and  carbon  which  is  most  effective  in  pro- 
tecting the  acid  lining  of  the  furnace  from  the  corrosive  action  of 
the  basic  slag. 

Hot  Blast.  —  The  air  for  smelting  is  driven  into  the  furnace  by 
immense  blowing  engines  ranging  up  to  2500  H.P.  each,  and  capable 
of  compressing  50,000  to  65,000  cu.  ft.  (=4875  Ib.1)  of  free  air  per 
minute  to  a  pressure  of  15  to  30  Ib.  per  sq.  in.,  which  is  about  what 
one  furnace  requires.  It  actually  requires  about  4  to  5  tons  of  air 
for  each  ton  of  iron  produced  in  the  furnace.  After  leaving  the 
engines  and  before  coming  to  the  furnace,  the  air  is  heated  to  a 
temperature  of  425  to  650°  C.  (800  to  1200°  F.),  by  being  made  to 
pass  through  the  hot-blast  stoves. 

Hot-blast  Stoves.  —  Each  furnace  is  connected  with  four  stoves. 
These  are  cylindrical  tanks  of  steel  about  110  ft.  high  and  22  ft.  in 
diameter,  containing  two  fire-brick  chambers.  One  of  these  cham- 
bers is  open,  and  the  other  is  filled  with  a  number  of  small  flues 
(see  Fig.  18) .  Gas  and  air  are  received  in  the  bottom  of  the  open 
chamber,  B,  in  which  they  burn  and  rise.  They  then  pass  down- 
ward through  the  several  flues  in  the  annular  chamber  surrounding 
B,  and  escape  at  the  bottom  to  the  chimney  as  waste  products.  In 
passing  through  the  stove  they  give  up  the  greater  part  of  their 
heat  to  the  brickwork.  After  this  phase  is  ended,  the  stove  is  ready 
to  heat  the  blast. 

The  blast  from  the  blowing  engine  enters  at  the  bottom  of  the 
flues,  E,  passes  up  through  the  outer  chamber,  and  down  through  B 
to  the  furnace.  •  In  this  passage  it  takes  up  the  heat  left  in  the 
brickwork  by  the  burning  gas  and  air.  Sometimes  there  are  three 
passes,  instead  of  two  as  described.  In  a  blast-furnace  plant  one 
stove  is  heating  the  blast  while  the  other  three  are  simultaneously 
in  the  preparation  stage,  burning  gas  and  air.  By  changing  once 
an  hour  a  pretty  regular  blast-temperature  is  maintained.  The  gas 
used  for  the  heating  is  the  waste  gas  from  the  blast  furnace  itself, 
which  amounts  to  about  90,000  cu.  ft.  per  minute  at  a  temperature 
of  235°  C.  (450°  F.) ,  and  has  a  calorific  power  of  about  85  to  95  B.  T. 
U .  per  cubic  foot.  The  latent  and  available  heat  of  this  gas  is  equiva- 
lent to  approximately  50  per  cent,  of  that  of  the  fuel  charged  into 

1  At  70°  F.  and  atmospheric  pressure,  each  1000  cu.  ft.  of  air  weighs  75  Ib. 


FIG.    18.  —  HOT-BLAST  STOVE.     From  Howe,  "Iron,  Steel  and  other  Alloys." 

Solid  arrows  show  passage  of  air  that  is  heating.     Broken  arrows  show  passage  of  burning 
gas.     This  is  but  one  of  several  types  of  stove. 

28 


FIG.  19. 


29 


30  THE   METALLURGY   OF   IRON   AND   STEEL 

the  furnace.  Only  about  30,000  cu.  ft.,  or  one-third  of  this  gas,  is 
needed  for  keeping  the  stoves  hot,  and  the  remaining  two-thirds  is 
used  to  produce  power. 

Power  from  Waste  Gas.  —  The  waste  gas  comes  down  the 
downcomer  T,  Fig.  19,  settles  out  dirt  in  the  dust-catcher  W ,  and 
is  then  led  to  the  stoves  or  power-producer.  This  gas  varies  in 
composition,  but  will  average  about  61  per  cent,  nitrogen,  10  to 
17  per  cent.  C02,  and  22  to  27  per  cent.  CO.  The  latter  can  be 
burned  with  air  to  produce  heat. 

CO  +  O-COa  (generates  68,040  calories). 

If  burned  under  boilers,  the  available  gas  will  generate  enough 
power  to  operate  the  blowing  engines,  hoisting  mechanism,  and 
other  machinery  used  in  connection  with  the  furnace.  At  several 
plants  the  gas  available  for  power  is  cleaned  carefully  and  utilized 
in  gas  engines,  whereby  much  more  power  is  obtained,  the  excess 
being  usually  converted  into  electricity  and  transmitted  to  more 
distant  points. 

SMELTING  PRACTICE  AND  PRODUCTS 

The  furnace  is  filled  with  alternate  layers  of  fuel,  flux,  and  ore, 
down  to  the  top  of  the  smelting  zone.  The  exact  location  of  this 
zone  will  be  dependent  upon  the  volume  and  pressure  of  blast,  size 
of  furnace,  character  of  slag  made,  etc.,  but  will  extend  from  the 
level  of  the  tuyeres  to  a  few  feet  above  them,  or  about  to  the  top  of 
the  bosh.  It  will  require  perhaps  15  hours  for  the  material  to  de- 
scend from  the  top  of  the  furnace  to  the  smelting  zone.  During 
this  descent,  it  is  upheld  partly  by  the  resistance  of  the  upward- 
rushing  column  of  hot  gases,1  partly  by  its  friction  on  the  walls  of 
the  furnace,  and  partly  by  the  loose  column  of  coke  which  extends 
through  the  smelting  zone  and  to  the  bottom  of  the  furnace,  and 
which  alone  resists  melting  in  the  intense  heat  of  this  zone.  The 
blast,  entering  the  furnace  through  the  tuyeres,  consists  of  23  per 
cent,  by  weight  of  oxygen  and  77  per  cent,  by  weight  of  nitrogen, 
together  with  varying  amounts  of  water  vapor  from  moisture  in 
the  air  (see  page  38).  The  nitrogen  is  practically  inert  chemically 
and  performs  no  -function  other  than  that  of  absorbing  heat  in  the 

1  There  is  a  great  fall  in  the  pressure  of  the  blast  between  the  tuyeres 
and  the  throat,  which  represents  the  work  done  by  the  air  in  helping  to  support 
-the  stock. 


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31 


32 


THE  METALLURGY  OF   IRON  AND   STEEL 


smelting  zone  and  giving  it  out  at  higher  levels.  The  oxygen 
attacks  all  the  coke  in  the  smelting  zone  and  as  much  of  it  below 
the  level  of  the  tuyeres  as  is  not  covered  by  accumulations  of  iron 


Fusion  Level 


Molten  Slag 
Molten  Iron 


Legend ;  —  Lumps  of  Coke 

Lumps  of  Iron  Ore ® 

Lumps  of  Lime O 

Drops  of  Slag _._d 

Drops  of  Iron I 

Layer  of  Molten  Slag 

Layer  of  Molten  Iron 

FIG.  21.     From  Howe,  "Iron,  Steel,  and  other  Alloys." 

and  slag  in  the  hearth,  producing  a  large  volume  of  carbon  mon- 
oxide gas  (CO)  and  a  temperature  of  about  1510°  C.  (2750°  F.).1 

1  It  is  of  minor  importance  whether  the  CO  gas  is  formed  directly  or  as  a 
result  of  the  two  following  reactions: 

C  +O2=CO3 
CO2  +  C    =2CO 


THE  MANUFACTURE   OF   PIG   IRON  33 

The  CO  and  nitrogen  pass  up  between  the  particles  of  solid  ma- 
terial, to  which  they  give  up  the  greater  part  of  their  heat.  The 
former  also  performs  certain  chemical  reactions,  and  thus  in  both 
ways  the  rising  column  of  gases  prepares  the  charge  for  its  final 
reduction  in  the  smelting  zone. 

Chemical  Reactions  in  the  Upper  Levels.  —  As  soon  as  the  iron 
ore  enters  the  top  of  the  furnace,  two  reactions  begin  to  take  place 
between  it  and  the  gases : 

(1)  2Fe2O3+8CO=7CO2+4Fe+C; 

(2)  2  Fe2O3+    CO  =2  FeO+Fe2Os+CO2; 

and  this  continues  with  increasing  rapidity  as  the  material  becomes 
hotter.  The  carbon  formed  by  reaction  No.  1  deposits  in  a  form 
similar  to  that  of  lampblack  on  the  outside  and  in  the  interstices  of 
the  ore.  This  reaction,  however,  is  opposed  by  two  reactions  with 
carbon  dioxide  gas : 

(3)  Fe+CO2=FeO+CO; 

(4)  C+CO2=2CO. 

Reaction  No.  3  begins  at  a  temperature  of  about  300°  C.  (575° 
F.),  which  is  met  with  about  3  or  4  ft.  below  the  top  level  of  the 
stock;  and  No.  4  begins  at  about  535°  C.  (1000°  F.),  or  20  ft.  below 
the  stock  line.  Reaction  No.  4  is  so  rapid  that  the  deposition  of 
carbon  ceases  at  a  temperature  of  590°  C.  (1100°  F.).  All  the  way 
down  the  ore  is  constantly  losing  a  proportion  of  its  oxygen  to  the 
gases.  At  higher  temperatures  than  590°  C.,  FeO  is  stable,  and 
practically  all  of  the  Fe2Os  (or  Fe304  if  magnetite  is  being  smelted) 
has  been  reduced: 

(5)  Fe3O4+CO  =3  FeO+CO2. 

The  reaction  between  iron  oxide  and  solid  carbon  begins  at  400° 
C.  (750°  F.). 

(6)  Fe2O3  +  3  C  =2  Fe  +  3  CO. 

At  700°  C.  (1300°  F.)  solid  carbon  begins  to  reduce  even  FeO: 

(7)  FeO+C=Fe+CO. 

Practically  all  the  iron  is  reduced  to  a  spongy  metallic  form  by 
the  time  the  temperature  of  800°  C.  (1475°  F.)  is  reached.  This  is 
about  45  ft.  from  the  stock  line  and  less  than  30  ft.  above  the 
tuj^eres.  At  800°  C.  the  limestone  begins  to  be  decomposed  by 
the  heat,  and  only  CaO  comes  to  the  smelting  zone : 

(8)  CaC03=CaO+COa. 


34  THE  METALLURGY  OF   IRON  AND   STEEL 

The  foregoing  facts  are  summarized  in  Fig.  22,  which  is  adapted 
from  H.  H.  Campbell,  with  certain  changes.1  It  is  not  supposed 
that  these  figures  are  exactly  correct  for  the  different  levels,  and  it 
is  probable  that  they  change  from  day  to  day  and  from  furnace  to 
furnace,  but  a  general  idea  may  be  obtained  from  this  sketch.  It 
will  be  seen  that  the  upper  15  or  20  ft.  of  the  stock  is  a  region  of 
Fe2O3  and  Fe3O4,  gradually  being  converted  to  FeO  by  CO  gas, 
and  forming  quantities  of  C02  gas.  If  these  reactions  were  the 
only  ones,  the  top  gases  would  contain  no  CO  and  would  have  no 
calorific  power,  but  reaction  No.  1  produces  both  metallic  iron  and 
carbon,  both  of  which  reduce  C02  and  waste  much  energy,  as  far  as 
the  blast  furnace  is  concerned: 

Reaction  No.  3,  Fe+CO2  =FeO+CO,  absorbs  2340  calories, 
but  wastes  68,040  calories. 

Reaction  No.  4,  C+CO2  =2  CO,  absorbs  38,880  calories. 

From  20  to  35  ft.  below  the  stock  line  is  the  region  of  FeO, 
gradually  being  converted  to  metallic  iron  sponge  by  carbon.  On 
the  lower  level  of  this  zone  the  limestone  loses  its  C02,  which  joins 
the  other  furnace  gases.  From  35  ft.  down  to  the  smelting  zone  is 
the  region  of  metallic  iron.  This  spongy  iron  is  impregnated  with 
deposited  carbon  which  probably  to  some  extent  soaks  into  it  and 
dissolves,  in  a  manner  like  in  nature  but  not  in  degree  to  the  way 
ink  soaks  into  blotting-paper.  This  carburization  of  the  iron 
reduces  its  melting-point  and  causes  it  to  become  liquid  at  a  higher 
point  above  the  tuyeres  than  it  otherwise  would. 

On  reaching  the  smelting  zone  the  iron  melts  and  trickles 
quickly  down  over  the  column  of  coke,  from  which  it  completes  its 
saturation  with  carbon.  At  a  corresponding  point  the  lime  unites 
with  the  coke  ash  and  impurities  in  the  iron  ore,  forming  a  fusible 
slag  which  also  trickles  down  and  collects  in  the  hearth.  It  is 
during  this  transit  that  the  different  impurities  are  reduced  by  the 
carbon,  and  the  extent  of  this  reduction  determines  the  character- 
istics of  the  pig  iron,  for  in  this  operation,  as  in  all  smelting, 
reduced  elements  are  dissolved  by  the  metal,  while  those  in  the 
oxidized  form  are  dissolved  by  the  slag.  Only  one  exception 
occurs,  namely,  that  iron  will  dissolve  its  own  sulphide  (FeS)  and, 
to  a  less  extent,  that  of  manganese  (MnS),  but  not  that  of  other 
metals,  as,  for  instance,  CaS. 

1  See  pp.  54  and  62  of  Book  No.  2,  page  8. 


THE   MANUFACTURE   OF   PIG   IRON 


35 


Chemical  Reactions  in  the  Smelting  Zone.  —  There  is  always  a 
large  amount  of  silica  present  in  the  coke  ash,  and  some  of  this  is 
reduced  according  to  the  reaction : 

(9)  SiO2+2C=Si+2CO. 

The  extent  of  this  reaction  will  depend  on  the  length  of  time  the 
iron  takes  to  drop  through  the  smelting  zone,  the  relative  intensity 
of  the  reducing  influence,  and  the  avidity  with  which  the  slag  takes 


Stock 

75-0      450°  F 

Line 

(1) 

(2) 

575°     (3) 

65  10     770°  F 

750°    W 

fj 

55  20   1090°F 

1025°     (4) 

1100° 

1300°     (7) 

45  30   1410°  F 

•«-  $ 

35  40   1730°F 

1830°     (4) 
p 

25-50  3050°F 

c» 

L5  60   2370°  F 

/ 
Smelting  j 

Tuyeres  - 

5  -70  Feet 
^.SftT. 

Zone  (J 

(1)  2Fe2O3  +  SCO  =  7CO2  4-  4Fe  +C  (begins) 

(2)  2Fe2O3+  CO=2FeO  +  CO3  +  Fe2O3  (begins) 

Fe    +    COa  =  FeO  +  CO    (begins) 
Fe9O3  +  3C  =  2Fe  +  SCO 

C     +     COQ  =  2CO       (rapid) 
Deposition  of  carbon  ceases 

FeO   +     C  =  Fe  +  CO    (begins) 

FeO    +     C  =  Fe  4-  CO    (complete) 
=      CaO  +  C0.2 


i)      C     +     C0a  =  2CO        (prevails) 
CO2  cannot  exist  below  this  level 


(9)    SiO.,  +  2C  =  Si  +  2CO 

(10)  FeS  +  CaO  +  C  =  CaS  +  Fe  +  CO 

(11)  MnO.,+  2G  =  Mn  +  20O 
P2O5   +  5C  =  2P  +  5CO 


FIG.  22.  — DIAGRAM  SHOWING  CHEMICAL  ACTION  IN  BLAST  FURNACE. 

up  silica.  A  slag  with  a  high  melting-point  will  trickle  sluggishly 
through  the  smelting  zone  and  cause  the  iron  to  do  the  same,  to 
some  extent,  thus  giving  it  more  chance  to  take  up  silicon.  A 
higher  temperature  in  the  smelting  zone,  which  increases  dispro- 
portionately the  avidity  of  carbon  for  oxygen,  will  promote  re- 
action No.  9.  We  can  produce  this  higher  temperature  by  supply- 


36  THE  METALLURGY   OF   IRON  AND   STEEL 

ing  hotter  blast.  A  larger  proportion  of  coke  to  burden1  will 
further  promote  this  reaction,  because  this  not  only  increases  the 
amount  of  the  reducing  agent,  but  also  raises  the  temperature  and, 
therefore,  the  chemical  activity  of  this  agent.  Thus  the  coke  has 
both  a  physical  and  a  chemical  influence  in  increasing  the  intensity 
of  the  reduction  in  the  smelting  zone.  A  basic  slag,  because  of  its 
avidity  for  silica,  will  oppose  reaction  No.  9;  it  is  one  of  the  princi- 
pal means  of  making  low-silicon  pig  iron.  This  is  in  spite  of  the 
fact  that  the  basic  slags  are  sluggish,  and  therefore  trickle  slowly 
through  the  smelting  zone,  thus  exposing  the  silica  longer  to 
reducing  influence,  and  also  increasing  the  temperature  of  the 
materials  in  this  zone  (1)  by  causing  them  to  pass  through  it  more 
slowly  and  absorb  more  heat,  and  (2)  by  reducing  the  level  of  the 
smelting  zone  nearer  to  the  tuyeres,  which  confines  the  intense 
temperature  to  the  smaller  area,  or,  in  other  words,  diminishes  the 
passage  of  heat  upward. 

Sulphur  comes  into  the  furnace  chiefly  in  the  coke.  It  is  partly 
in  the  form  of  iron  sulphide  (FeS) ,  and  partly  in  the  form  of  iron 
pyrites  (FeS2) ,  which  loses  one  atom  of  sulphur  near  the  top  of  the 
stock  and  becomes  FeS,  which  will  dissolve  in  the  iron  unless  con- 
verted to  sulphide  of  calcium  (CaS).  This  is  brought  about,  ac- 
cording to  the  explanation  of  Professor  Howe,  by  the  following 
reaction: 

(10)  FeS+CaO+C=CaS+Fe+CO. 

CaS  passes  into  the  slag,  and  the  odor  of  sulphur  is  very  strong 
when  the  slag  is  running  from  the  furnace.  It  is  evident  from 
reaction  No.  10  that  intense  reduction,  which  increases  the  silicon 
in  the  iron,  has  the  contrary  effect  on  the  sulphur,  and  this  explains 
the  common  observation  that  iron  high  in  silicon  is  liable  to  be  low 
in  sulphur.  Indeed,  this  relation  is  so  constant  that  it  is  almost  a 
rule.  There  are  two  exceptions,  however:  (1)  Increasing  the 
proportion  of  coke  has  a  doubly  strong  influence  in  putting  silicon 
in  the  iron.  As  regards  sulphur,  on  the  other  hand,  it  has  a  self- 
contradictory  effect;  by  increasing  the  amount  of  sulphur  in  the 
charge  it  tends  to  increase  it  in  the  iron,  which  is  partly  or  wholly 
counteracted  by  its  effect  in  reaction  No.  10.  (2)  A  basic  slag  may 
hold  silicon  from  the  iron,  and  it  also  holds  sulphur  from  the  iron  by 
dissolving  CaS  more  readily.  In  other  respects  the  conditions 

1  The  burden  is  the  amount  of  material  that  the  coke  has  to  melt.     We 
Tighten  the  burden  by  increasing  the  amount  of  coke,  and  vice  versa. 


THE  MANUFACTURE   OF   PIG   IRON 


37 


TABLE  II.— COMPOSITION  OF   BLAST-FURNACE  SLAGS 
From  H.  H.  Campbell.  P.  50  of  No.  2. 


SLAG 

IRON 

REMARKS 

1 

2 

3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 

It) 
17 
18 
11) 
20 
21 
22 
23 
24 
25 
26 

SiO2 

A1202 

CaO 

MgO 

FeO 

S 

Total 
not  in- 
clud- 
ing S 

Si 

S 

tr. 
tr. 
.01 
.06 
.11 
.05 
.03 
.02 
.02 
.02 
tr. 
.02 
.03 
.03 
.07 
.020 
.029 
.028 
.032 
.017 
!040 
.095 
.101 
.048 
.038 
.034 

tr. 
.025 
.020 
.027 

.07 
.03 
.063 
.040 

33.10 
32.27 
24.26 
32.68 
32.28 
34.50 
34.98 
34.70 
33.68 
29.86 
28.95 
30.62 
32.55 
30.08 
31.46 
36.08 
37.19 
36.86 
32.06 
33.57 
35.38 
36.35 
33.70 
35.11 
35.10 
35.84 

Avera 

33.21 
34.84 
31.77 
35.55 
A.vera 
33.15 
30.73 
34.75 
35.35 

14.9240.76 
14.57  41.02 
11.5340.25 
13.50  43.28 
9.38  46.95 
7.94  46.47 
12.05  41.33 
11.4441.27 
11.9345.96 
12.0445.20 
12.0449.30 
10.4749.13 
11.1347.16 
11.4446.36 
11.5044.85 
12.8541.69 
12.65  35.47 
10.7442.46 
11.9742.46 
10.6544.11 
11.7638.19 
10.2140.10 
12.5638.12 
14.21  22.48 
14.75  27.95 
14.34  32.71 
ges  for  hot  i 

13.67(40.68 
11.75|41.30 
11.9845.58 
12.0540.52 
»es  for  modt 
10.27  45.57 
11.3247.36 
11.3040.12 
14.43  29.69 

9.67 
10.30 
13.28 
9.44 
9.52 
10.47 
9.62 
9.96 
6.69 
11.41 
8.46 
7.49 
6.61 
8.76 
10.41 
7.25 
11.32 
6.62 
10.25 
8.55 
12.32 
10.95 
11.60 
22.38 
22.28 
17.46 
urnac 
11.08 
9.79 
9.05 
8.86 
jrate  ( 
9.81 
8.35 
10.86 
20.71 

98.45 
98.16 
98.32 
98.90 
98.13 
99.38 
97.98 
97.37 
98.26 
98.51 
98.75 
97.71 
97.45 
96.64 
98.22 
98.41 
97.53 
97.31 
97.37 
97.69 
98.53 
98.60 
98.30 
100.12 
100.08 
100.35 

98.64 
97.68 
98.38 
97.66 
•nace  : 
98.80 
97.751 
98.29 
100.18! 

3.37 

3.18 
4.81 
1.25 
0.70 
0.69 
2.60 
2.32 
1.27 
1.27 
0.57 
0.26 
0.15 
0.58 
0.20 
2.15 
1.92 
1.50 
1.59 
0.94 
1.13 
0.66 
0.50 
1.37 
1.85 
1.60 

3.79 
2.46 
1.27 
1.79 

0.88 
0.35 
0.81 
1.61 

Cuban  ore,  He 

it                 ( 

{(                 { 
Wz 
]              C°,( 
Spanish  ore,  P 

Cc 

1  Lake  ore 
1  and  part 
|  anthracite 
J^coal; 
mostly 
Connells- 
ville  coke 

1  Lake  ore 
•  and  Con-     - 
J  nellsville 
coke. 

Cuban  ore. 
Spanish  ore. 

ie            (( 

Lake  ore. 

Cuban  ore. 
Spanish  ore. 
Lake  ore. 

>t  furnace 

irm   ' 

>1         < 

i        t 
tot  furnace 

)0l 

Hot  furnace 
Fairly  hot 

Normal 
u 

Cool 

I     " 
[Av.  of  8  wks 
Av.  of  7  wks 
Av.  of  7  wks 

.  . 

.. 
0.54 
0.90 
0.63 
0.63 
0.81 
0.90 
0.99 
0.32 

1.62 
1.70 
1.54 
1.76 
1.74 
1.60 
1.28 
0.96 

es: 

.... 

,0.68  1.66 
>r  cool  fui 

l'.26 

i'.io 

which  make  for  high  silicon  make  also  for  low  sulphur.  Particu- 
larly is  this  true  of  a  high  temperature  in  the  smelting  zone,  and 
the  term  'hpt  iron'  has  come  to  be  synonymous  in  the  minds  of 
blast-furnace  foremen  with  iron  high  in  silicon  and  low  in  sulphur. 


38  THE   METALLURGY   OF   IRON   AND   STEEL 

Manganese  is  reduced  by  the  following  reaction : 
(11)  MnO2+2  C  =  Mn+2  CO. 

The  amount  of  manganese  in  the  iron  is  dependent,  to  a  certain 
extent,  upon  the  character  of  the  ores  charged,  but  it  may  be  con- 
trolled somewhat  by  the  character  of  slag  made,  because  an  acid 
slag  will  carry  a  large  amount  of  manganese  away  in  the  form  of 
silicate  of  manganese  (MnSiO3) . 

With  a  certain  unimportant  qualification,  the  amount  of  phos- 
phorus in  the  iron  is  controlled  by  the  character  of  the  ores  charged, 
and  districts  or  countries  having  high-phosphorus  ores  must  make 
high-phosphorus  irons.  This  is  not  an  insuperable  objection,  be- 
cause the  presence  of  phosphorus,  even  up  to  1.5  per  cent.,  is 
desired  in  certain  irons  for  foundry  use,  and  the  basic  processes  for 
making  steel  can  remove  this  element. 

The  chemical  influence  of  the  blast  furnace  is  a  strongly  redu- 
cing one,  and  this  is  produced  in  order,  first,  to  reduce  the  iron  from 
the  ore;  second,  to  get  rid  of  the  sulphur,  and  third,  to  saturate  the 
iron  with  carbon.  Many  attempts  have  been  made  to  provide  a 
process  wherein  the  reducing  influence  was  not  so  strong,  and  thus 
to  produce  a  purer  material  than  pig  iron,  because  it  is  the  intensity 
of  the  reduction  which  vitiates  the  iron  with  carbon  and  silicon. 
The  great  weakness  of  all  such  processes,  however,  is  that  they  do 
not  get  rid  of  the  sulphur,  which  is  the  most  objectionable  impurity 
that  iron  is  liable  to  contain  and  which  is  not  satisfactorily  re- 
moved by  any  process  after  once  it  makes  its  way  into  the  iron. 
Finally,  to  saturate  the  iron  with  carbon  renders  the  blast-furnace 
operation  very  much  cheaper,  because  pure  iron  melts  at  a  tem- 
perature much  higher  than  can  readily  be  obtained  in  the  furnace, 
and  melted  iron  is  handled  much  more  cheaply  than  it  could  be  if 
allowed  to  solidify.  Even  the  presence  of  silicon  is  an  advantage, 
as  we  shall  see  in  Chapter  XII. 

Drying  the  Blast.  —  The  water  vapor  blown  into  the  furnace 
(derived  from  the  moisture  of  the  air)  is  equivalent  to  from  J  to  2 
gal.  of  water  per  10,000  cu.  ft.  of  blast,  or  1J  to  8  gal.  per  minute, 
depending  on  the  humidity  of  the  atmosphere".  Though  this  steam 
is  as  hot  as  the  blast,  it  materially  cools  the  smelting  zone  of  the 
furnace  by  dissociating  there: 

=  2  H+CO  (absorbs  28,900  gram  calories); 


THE  MANUFACTURE  OF  PIG  IRON  39 

or  1  Ib.  of  steam  absorbs  7,110,000  calories.  The  hydrogen  and 
oxygen  reunite  in  a  cooler  part  of  the  furnace  and  return  the  same 
amount  of  heat,  but  this  does  not  compensate  for  that  taken  away 
from  the  smelting  zone,  where  it  is  most  needed.  For  this  reason 
a  few  American  plants,  and  at  least  one  in  England,  have  adopted 
James  Gayley's  expedient  of  drying  the  air  by  refrigeration  before 
it  is  drawn  into  the  blowing  engine.  This  results  in  greater  regu- 
larity of  furnace  working  and  valuable  saving  in  fuel.  In  fact,  so 
great  is  the  economy  shown  in  this  respect  that  there  was  a  tend- 
ency at  first  to  receive  the  results  with  skepticism.  J.  E.  Johnson, 
Jr.,  has  explained  this  saving,  however,  in  a  very  ingenious  and 
skillful  manner,  by  showing  that  every  blast  furnace  has  a  certain 
'critical  temperature/  below  which  it  will  not  perform  any  smelt- 
ing, and  that  the  theoretical  temperature  of  combustion  of  the 
smelting  zone  is  only  a  little  above  this  'critical  temperature.' 
To  increase  this  small  interval  between  the  two,  therefore,  greatly 
increases  the  'available  heat/  though  the  change  in  nominal  tem- 
perature be  small.1 

Slag  Disposal.  —  On  account  of  its  lower  specific  gravity,  the 
slag  floats  on  top  of  the  bath  of  iron  in  the  hearth  and  accumu- 
lates, frequently  until  it  reaches  the  bottom  level  of  the  tuyeres. 
Four  or  five  times  every  six  hours  the  plug  in  the  cinder-notch  is 
pierced  with  a  steel  rod  and  the  cinder  above  this  level  allowed  to 
run  out.  It  flows  down  an  inclined  iron  runner  for  a  distance  of 
15  to  30  ft.  and  pours  into  an  iron  ladle  on  a  standard-gage  railroad 
track,  whence  it  is  drawn  away  by  a  locomotive  and  poured  out  on 
the  slag  dump.  Slag  varies  in  composition  according  to  the  will  of 
the  blast-furnace  manager,  and  some  typical  analyses  are  given  in 
Table  II.  Slags  high  in  lime  are  sometimes  treated  with  addi- 
tional lime  to  make  a  good  grade  of  Portland  cement,  known  as 
'Puzzolini.'  The  amount  of  cinder  made  will  depend  on  the 
amount  of  silica,  alumina,  etc.,  in  the  ore,  the  amount  of  coke  ash, 
and  the  amount  of  flux,  which  will  also  depend  on  the  desired  slag 
analysis.  Under  favorable  circumstances,  the  slag  may  weigh 
slightly  less  than  half  the  iron;  under  other  conditions  it  may  weigh 
nearly  twice  the  iron. 

1  If  further  explanation  of  this  argument  is  needed,  it  may  be  found  in  the 
following  simile:  Water  boils  at  212°  F.  If  the  temperature  of  a  boiler  is  262°, 
there  is  a  certain  pressure  of  steam ;  if  we  increase  the  temperature  only  50°,  we 
greatly  increase  the  pressure;  yet  50°  appears  small  in  comparison  to  262°. 


40  THE  METALLURGY   OF   IRON   AND   STEEL 

Weight  of  Slag.  —  The  amount  of  slag  may  be  calculated  from 
the  amount  of  lime  (CaO)  in  the  furnace,  which  may  be  calculated 
from  the  percentage  of  lime  in  the  limestone  and  other  materials 
charged  into  the  furnace.  Since  all  the  lime  charged  goes  into  the 
slag,  the  amount  of  the  latter  will  be  equal  to  the  weight  of  lime 
divided  by  the  percentage  of  the  lime  in  the  slag.  Thus,  if  we  use 
per  ton  of  iron  1300  Ib.  of  limestone,  containing  50  per  cent,  of 
lime,  there  will  be  650  Ib.  of  lime  charged  for  every  ton  of  iron 
made.  If  the  slag  made  contains  40  per  cent,  lime,  then  the  weight 
of  slag  will  be  ^j5/  =  1625  Ib.  per  ton  of  iron  made. 

Iron  Disposal.  —  Immediately  after  the  last  'flushing/  i.e.,  re- 
moval of  cinder,  the  tap  hole  or  iron  notch  is  opened  by  several 
men  "drilling  a  hole  in  it  with  a  heavy,  pointed  steel  bar.  Out  of 


FIG.  23. 

this  notch  flows  100  to  150  tons  of  liquid  pig  iron,  with  which  is 
carried  along  30  tons  or  so  of  slag.  The  'skimmer'  is  situated 
about  a  dozen  feet  from  the  front  of  the  furnace.  It  is  an  iron 
plate  extending  down  almost  to  the  -bottom  of  the  runner.  The 
slag  is  deflected  by  this  plate  into  a  runner  of  its  own,  which  leads  it 
off  to  a  slag  ladle  such  as  described  before.  The  heavier  pig  iron 
flows  under  the  skimmer  and  is  distributed  to  six  or  seven  brick- 
lined  ladles  on  a  standard-gage  railroad  track.  It  is  then  drawn 


THE  MANUFACTURE   OF   PIG  IRON 


41 


away  to  the  steel  works,  or,  if  not  wanted  there,  is  poured  into  iron 
molds  at  the  pig-casting  machine. 

Mechanical  Pig-Molding  Machine.  —  There  are  several  types  of 
molding  machine,  but  a  common  form  is  illustrated  in  Figs.  24-5,  and 
consists  of  a  long  continuous  series  of  hollow  metallic  molds  car- 


FIG.  24.  —  UEHLING  PIG-CASTING  MACHINE. 

ried  on  an  endless  chain.  D  is  the  pig-iron  ladle  pouring  metal  into 
the  spout,  from  whence  it  overflows  into  the  molds  as  they  travel 
slowly  past.  The  pig  iron  chills  quickly  against  the  metallic 
molds,  and  by  the  time  it  reaches  the  other  end  of  the  machine,  it 
consists  of  a  solid  pig  of  iron  which  drops  into  the  waiting  railroad 


FIG.  25.  —  HEYL  AND  PATTERSON  PIG-CASTING  MACHINE. 

car  as  the  chain  passes  over  the  sheave.  The  pig  iron  is  now  in  a 
form  convenient  for  transportation  or  for  storing  until  needed. 
The  molds  travel  back  toward  the  spout,  underneath  the  machine 
and  hollow  side  down.  At  the  point  C  they  are  sprayed  with 
whitewash,  the  water  of  which  is  quickly  dried  off  by  the  heat  of  the 
mold,  leaving  a  coating  of  lime  inside  to  which  the  melted  iron  will 


42 


THE   METALLURGY  OF   IRON   AND   STEEL 


not  stick.  This  mechanical  casting  is  a  great  improvement  over 
the  former  method  of  cooling  iron  in  front  of  the  blast  furnace, 
because  of  the  severity  of  the  work  which  the  former  method  in- 
volved and  which,  in  hot  weather,  was  well-nigh  intolerable  to 
human  beings.  It  also  gives  pigs  which  are  cleaner,  i.e.,  freer  from 
adhering  sand.  This  silicious  sand  is  objectionable,  especially  in 
the  basic  open-hearth  furnace. 

Sand-Casting.  —  This  method  is  still  used  at  some  furnaces, 
because  of  the  capital  needed  to  install  machines  and  their  high 
cost  for  repairs.  Moreover,  foundrymen  often  prefer  the  sand-cast 

pig  because  they  are  able  to 
tell  by  the  appearance  of  its 
fracture  what  grade  of  castings 
it  will  make,  which  they  cannot 
well  do  with  iron  cast  in  metal 
molds  (see  pages  336,  337). 
In  the  sand  method,  the  cast 
house  extends  in  front  of  the 
furnace  and  its  floor  is  com- 
posed of  silica  sand,  in  which 
the  molds  or  impressions  to 
receive  the  liquid  iron  are 
made.  The  main  runner  ex- 
tends from  the  taphole  down 
the  middle  of  the  floor,  and 
the  space  on  either  side  of  it  is 
used  alternately  for  alternate 
castings.  The  plan  of  the  ar- 
rangement is  shown  in  Fig.  26. 
After  cooling  the  iron,  the 
pigs  are  broken  away  from  the 
sows,  which  are  also  broken 
into  pieces  with  a  sledge,  and 
then  all  is  carried  over  and 

thrown  into  a  railroad  car.  In  making  '  basic  iron/  — i.e.,  iron  for 
the  basic  open-hearth  steel  process,  —  the  molds  for  the  sows  and 
pigs  are  permanently  made  of  metal,  so  that  the  iron  will  not 
carry  acid  sand  into  the  basic  hearth. 

Irregularities  in  Blast-Furnace  Working.  —  Although  the  man- 
agement and  control  of  the  operation  is  in  general  as  I  have  de- 


11 


1 


FIG.  26.  —  SAND-CASTING  BED. 


THE   MANUFACTURE   OF   PIG   IRON 


43 


scribed  it,  the  blast  furnace  is  by  no  means  a  perfect  machine,  and 
great  difficulties  arise  in  the  working  of  the  furnace  and  in  main- 
taining a  uniform  grade  of  product.  The  chief  of  these  difficulties 


FIG.  27.  —  PIG  BEDS. 


44  THE   METALLURGY  OF   IRON  AND   STEEL 

result  from  localized  chilling  of  the  semi-molten  charge.  This  is 
most  liable  to  happen  in  the  upper  part  of  the  smelting  zone,  where 
a  little  lump  of  pasty  material  may  attach  itself  to  the  walls  of  the 
furnace.  This  has  the  effect  of  hindering  the  descent  of  that  part 
of  the  charge  above  it  and  of  deflecting  the  hot  gases  to  other  parts 
of  the  furnace.  The  result  of  the  first  action  is  to  disarrange  the 
order  and  evenness  with  which  originally  horizontal  rings  of  stock 
come  down  into  the  hearth.  The  obstruction  is  also  liable  to  re- 
ceive chilled  materials  from  above  and  to  build  itself  out  toward 
the  center.  When  the  furnace  is  working  badly,  these  scaffolds  may 
occur  at  two  or  more  places  at  the  same  time  and  cantilever  out 
toward  the  middle.  This  will  cause  a  'hanging'  of  the  charge,  and 
may  become  so  bad  as  to  cause  a  complete  arch  over  the  smelting 
zone,  through  which  it  is  impossible  to  drive  the  blast.  Sometimes 
the  scaffold  may  be  broken  down  by  suddenly  cutting  off  the  blast 
pressure  and  allowing  the  full  weight  of  material  in  the  furnace  to 
come  upon  the  obstruction;  but  sometimes  it  is  necessary  to  cut  a 
hole  in  the  wall  of  the  furnace  and  melt  it  out  with  a  blow-pipe 
burning  oil  or  gas,  or  with  some  other  form  of  heat. 

The  i  scaffolding7  of  a  furnace  and  hanging  of  the  charge  is  more 
liable  to  happen  when  large  percentages  of  the  earthy  Mesabi  ores 
are  used,  and  in  this  type  of  practice  localized  hanging  and  slips 
are  not  infrequent.  When  the  slip  is  extensive  in  character  and  a 
large  amount  of  material  is  suddenly  precipitated  into  the  hearth, 
the  upward  rush  of  gases  resembles  an  explosion  inside  the  furnace 
and  may  do  damage  to  the  charging  apparatus  and  throw  a  part  of 
the  stock  out  of  the  top  of  the  furnace.  Some  furnaces  are  pro- 
vided with  explosion  doors,  which  fly  open  under  pressure  and 
relieve  the  strain;  while  the  practice  in  other  instances  is  to  fasten 
everything  down  as  tight  as  possible  and  prevent  the  rapid  escape 
of  the  gases. 

There  is  also  a  large  amount  of  hanging  due  to  the  action  of  the 
blast  in  tending  to  drive  the  stock  before  it  up  into  the  stack  of  the 
furnace  and  thus  compress  it.  This  action  is  more  liable  to  take 
place  with  fine  ores 

Cooling  of  the  charge,  also,  results  in  some  cases  in  the  freezing 
of  material  over  the  mouths  of  the  tuyeres.  The  solid  layer  may 
sometimes  be  broken  away  with  a  bar,  and  the  blow  thus  allowed 
to  continue  until  more  heat  can  be  brought  down  into  the  hearth. 
Sometimes  it  is  necessary  to  melt  out  the  frozen  material  with  a 


THE  MANUFACTURE  OF  PIG  IRON  45 

blow-pipe,  and  in  extreme  cases  it  may  even  be  necessary  to  break 
through  it  with  explosives. 

Another  difficulty  sometimes  met  with  is  the  freezing  up  of  the 
metal  in  the  lower  part  of  the  hearth,  so  that  it  is  impossible  to 
open  the  tap-hole.  Then  a  new  tap-hole  must  be  made  by  boring 
through  the  front  of  the  furnace  at  a  higher  level,  from  which  the 
iron  is  drained,  and  then  the  heat  gradually  worked  down  until  the 
whole  hearth  is  melted  out  and  normal  conditions  reestablished. 
The  bad  work  of  a  furnace  is  often  cumulative  in  its  effects,  because 
irregularities  in  the  smelting  zone  have  an  effect  upon  the  top  gases, 
which,  in  turn,  derange  the  work  of  the  stoves  and  hence  impair 
the  hot  blast. 

These  irregularities  in  the  smelting  have  a  disturbing  effect  upon 
the  character  of  the  iron  made,  and  the  changes  sometimes  come 
suddenly  and  without  warning.  For  instance,  a  sudden  precipita- 
tion of  cold  material  into  the  hearth  will  chill  the  smelting  zone  and 
cause  the  silicon  in  the  iron  to  be  low  and  the  sulphur  high.  The 
same  effect  will  be  produced  by  the  leakage  of  several  gallons  of 
water  into  the  hearth  through  the  burning  out  of  a  tuyere  or  the 
cooling-ring  of  one  of  the  tuyeres.1 

Dimensions  of  Blast  Furnace.  —  The  size  of  a  modern  blast 
furnace  is  limited  by  the  conditions  of  its  work:  the  hearth  may 
not  be  much  more  than  15  ft.  in  diameter,  else  the  blast  from  the 
tuyeres  will  not  be  distributed  evenly  to  the  center;  the  batter  of 
the  bosh  walls  cannot  be  much  more  nor  less  than  a  certain  amount, 
because  they  must  give  support  to  the  charge  above  them,  and  yet 
allow  the  solid  coke  to  slip  down;  the  height  of  bosh  is  limited,  be- 
cause its  top  must  be  practically  the  same  as  the  top  of  the  smelting 
zone,  —  that  is,  no  solid  material  except  coke  should  descend  into 
the  bosh.  These  conditions  therefore  limit  the  diameter  of  the 
top  of  the  bosh  to  not  much  more  than  22  ft.  From  the  bosh  the 
stack  walls  must  decrease  in  diameter  upward  in  order  that  the 
descending  charge,  which  swells  in  the  reactions  that  take  place 
from  the  throat  downward,  shall  not  become  wedged  in  the  stack; 

1  In  iny  early  days  at  the  blast  furnace  I  was  once  informed  by  the  assist- 
ant manager  that,  on  one  occasion,  he  tapped  several  tons  of  water  from  the 
tap-hole  with  the  iron.  Whether  he  was  himself  deceived  or  whether  he  was 
merely  trying  to  test  me,  I  have  never  been  able  to  decide;  but  the  fact  is 
worthy  of  mention  in  an  elementary  treatise  to  illustrate  the  character  of  the 
tales  to  which  even  the  educated  men  around  a  plant  will  treat  a  novice. 


46 


THE   METALLURGY   OF   IRON   AND   STEEL 


as  the  throat  must  have  a  sufficiently  large  diameter  to  properly 
charge  the  materials,  this  limits  the  height  of  the  stack.  Modern 
furnaces  are  therefore  usually  built  about  90  ft.  in  height,  and  the 
exceeding  of  that  limit  has  resulted  in  some  cases  in  a  decrease, 
rather  than  an  increase  of  fuel  economy. 


CALCULATING  A  BLAST-FURNACE  CHARGE 

This  subject  is  of  prime  importance  to  young  metallurgists, 
because  the  ability  to  calculate  a  charge  is  sometimes  a  cause  of 
advancement,  and  the  knowledge  of  the  way  to  do  so  is  not  always 
obtainable  from  one's  superior. 

Assumptions.  —  Let  us  assume  that  we  desire  to  produce  a  slag 
containing  55  per  cent,  lime,  15  per  cent,  alumina,  and  30  per  cent, 
silica,  these  proportions  being  determined  by  the  experience  of  the 
manager,  and  that  the  materials  from  which  the  charge  is  to  be 
made  analyze  according  to  Table  III.  Assume  furthermore  that 
the  coke  ash  is  equal  to  10  per  cent,  of  the  coke,  and  that  the  iron 
we  are  going  to  make  will  contain  about  1  per  cent,  silicon. 

TABLE  III 


MATERIAL 

Per  cent. 
CaO 

Per  cent. 
MgO 

Per  cent. 
A1203 

Per  cent. 
SiO8 

Per  cent. 
Fe203 

Per  cent. 
Fe 

Ore  A  
Ore  B 

5 
2 

3 

2 
12 

11 
16 



60 

50 

Coke  ;i  sh 

20 

18 

50 

10 

Limestone 

46 

3 

2 

4 

2 

Silicon  in  the  Iron.  —  This  last  assumption  necessitates  our 
allowing  a  corresponding  amount  of  silica,  because  the  silica 
reduced  and  absorbed  by  the  iron  will  not  be  available  for  slag- 
making  purposes.  One  per  cent,  of  silicon  is  roughly  equal  to  2 
per  cent,  of  silica ;  we  may  therefore  make  the  requisite  allowance 
by  subtracting  from  the  silica  in  each  material  an  amount  equiva- 
lent to  2  per  cent,  of  its  iron  content.  Thus  we  begin  to  make  up 
Table  IV. 

Magnesia.  —  In  considering  slags,  magnesia  is  classified  under 
the  head  of  lime.  We  cannot  do  this,  however,  by  a  simple  addi- 
tion of  the  figures  of  the  percentages,  because  1  per  cent,  of  mag- 


THE  MANUFACTURE  OF  PIG  IRON 


47 


jiesia  will  do  the  chemical  work  of  1.4  per  cent,  of  lime,  on  account 
of  the  difference  in  molecular  weight  (CaO  =  56 ;  MgO  =  40) .     Thus : 

CaO  +  SiO2  =  CaSiO3; 
MgO  +  SiO2  =  MgSiOs. 

We  thus  multiply  each  percentage  of  magnesia  by  1.4  and  add 
the  product  thus  obtained  to  the  percentage  of  lime  in  each  ma- 
terial, thus  obtaining  column  2  in  Table  IV. 

TABLE  IV 


MATERIAL 

Per  cent. 
CaO 

Per  cent. 
A1203 

Per  cent. 
SiOa 

Ore  4                    

9 

2 

10 

Ore  B                         

2 

12 

15 

Coke  ash               

20 

18 

50 

Limestone          

50 

2 

4 

Self  fluxing  of  Materials.  —  It  is  evident  that  in  so  far  as  each 
of  the  materials  in  Table  IV  contains  all  the  components  of  the  slag, 
they  will  partially  flux  themselves.  For  example,  the  2  per  cent, 
of  alumina  in  ore  A  will  theoretically  combine  with  4  per  cent,  of 
the  silica  (2  per  cent.  X-f-J  =4  per  cent.)  and  7  per  cent,  of  the  lime 
(2  per  cent.  X-j-j-  =  7.3  per  cent.)  to  make  a  slag  of  the  desired  pro- 
portions, leaving  unfluxed  percentages  as  per  the  first  line  of  Table 
V.  In  the  same  manner  we  may  use  up  all  of  the  lime  in  ore  B  by 
uniting  it  with  weights  of  alumina  and  silica  in  proportion  to  the 
percentages  of  these  components  in  the  slag.  Similar  simplifica- 
tions in  the  analyses  of  coke  ash  and  limestone  may  then  be  calcu- 
lated, and  Table  V  will  be  completed. 

TABLE  V 


MATERIAL 

Per  cent. 
CaO 

Per  cent. 
A1203 

Per  cent. 
SiOa 

Ore  A 

2 

6 

Ore  B 

11  5 

14 

Coke  ash 

13  0 

39 

Limestone 

43 

Weight  of  Charge.  —  Let  us  assume  that  we  are  going  to  make 
one  ton  of  pig  iron  for  every  ton  of  coke  used  in  the  charge,  and 
that  the  coke  will  be  put  in  in  charges  weighing  11,000  Ib.  each. 
This  weight  includes  about  10  per  cent,  of  moisture,  dust,  etc.,  so 


48 


THE  METALLURGY   OF   IRON  AND   STEEL 


we  calculate  with  it  as  if  it  weighed  only  10,000  Ib.  Now  let  us 
determine  how  much  ore  will  be  put  in  each  charge:  The  ores 
average  55  per  cent,  of  iron;  therefore,  g  I 0p£0J»t  =  18,000  Ib.,  the 
amount  of  ore  that  must  be  in  each  charge,  according  to  the  assump- 
tion of  this  paragraph. 

Adjusting  the  Alumina  and  Silica.  —  Next  adjust  the  different 
materials  so  that  the  weight  of  alumina  shall  be  -J-§-  of  the  weight  of 
silica.  In  the  first  rough  approximation  of  this  we  may  neglect  the 
coke  ash,  because  the  weight  of  this  ash  is  so  small  in  relation  to 
the  other  materials.  Therefore  only  the  two  ores  need  be  appor- 
tioned, and  we  quickly  find  by  trying  a  few  mixtures  at  random 
that  60  per  cent,  of  ore  A  mixed  with  40  per  cent,  of  ore  B  will  give 
the  desired  relation  i1  60  per  cent.  X  6  +  40  per  cent.  X 14  =  920  parts 
of  silica;  60  per  cent. XO  +  40  per  cent. Xl  1.5  =460  parts  alumina; 
4}jj  =£|.  Now  draw  Table  VI,  and  enter  10,800  Ib.  of  ore  A  ( =60 
per  cent,  of  18,000),  7200  Ib.  of  ore  B,  1000  Ib.  of  coke  ash  (  =  10 
per  cent,  of  10,000),  and  the  percentages  from  Table  V.  All  the 
weights  in  this  table  may  then  be  filled  in  except  those  of  the  lime- 
stone and  total  CaO. 

To  obtain  the  total  number  of  pounds  of  lime : 

A12O3:  958  X  fl!  =  3513  Ib. 
SiO2:  2046  X  M  =  3751  Ib. 
Average  of  3515  and  3751  is  3632. 


TABLE  VI 


MATERIAL 

C* 

iO 

A13( 

>3 

Si< 

3a 

Weight. 

Per 

Cent. 

Lb. 

Per 
Cent. 

Lb. 

Per 
cent. 

Lb. 

Ore  A    

10,800 

2 

216 

6 

648 

Ore  B 

7200 

11   5 

828 

14 

1008 

Coke  ash 

1  000 

13  0 

130 

39 

390 

Limestone  

C 

7,940 

43 

B 

3416 

Total  Ib  

A 
3632 

958 

2046 

1  Try  first  50  per  cent,  of  each,  and  we  see  that  there  is  too  much  alumina; 
therefore  try  less  than  50  per  cent,  of  the  ore  having  the  most  alumina,  and 
correspondingly  more  of  the  other,  and  we  have  it. 


THE   MANUFACTURE   OF   PIG   IRON 


49 


Adjusting  for  Lime.  —  It  is  now  only  necessary  to  determine  the 
amount  of  total  lime  that  shall  bear  the  correct  relation  to  the 
alumina  and  silica  calculated.  This  we  do  by  means  of  the  method 
shown  in  the  figures  above  Table  VI.  We  enter  this  in  the  square 
'  A '  of  Table  VI.  The  figures  at  the  square  '  B '  are  then  obtained 
(3632  —  216=3416),  and  thence  the  weight  of  limestone  to  be  used 
—  (3416^-43  per  cent.  =7940). 

Checking  the  Calculations.  —  We  now  check  up  all  the  calcula- 
tions by  making  up  Table  VII,  in  which  we  go  back  to  the  original 
percentages  found  by  chemical  analysis  and  given  in  Table  III. 
In  making  up  this  final  table,  however,  we  use  our  experience  in 
making  slag  calculations  and  estimate  slight  changes:  For  ex- 
ample, Table  VI  shows  us  that  the  alumina  comes  a  little  low  in 
relation  to  silica;  therefore  we  increase  ore  B,  say,  by  400  Ib.  and 
decrease  ore  A  correspondingly.  But  ore  A  is  high  in  lime;  there- 
fore we  use  a  little  more  limestone  to  offset  this  reduction. 

TABLE  VII 


MATERIAL 

CaO  +  MgO 

Ai20s 

Si02 

Fe 

Weight. 

Per 
cent. 

Lb. 

Per 

cent. 

Lb. 

Per 
cent. 

Lb. 

Per 
cent. 

Lb. 

Ore  A      

10400 
7600 
1000 
8200 

9 
2 
20 
50 

936 
152 
200 
4100 

2 
12 
18 
2 

208 
912 
180 
164 

11 
16 
50 

4 

1144 
1216 
500 
328 

60 
50 
10 
2 

6240 
3800 
100 
164 

Ore  B  

Coke  ash  
Limestone  

Total  weights  

*4 

5388 

3  per 
t. 

1464 

=  14.  9  per 
cent. 

.  .3188  10,304 
-206(=2%X10,304) 

cen 

2982=30 

.  3  per  cent. 

These  figures  are  much  closer  to  those  desired  than  the  limit  of 
accuracy  in  furnace  operation.  The  chief  difference  is  that  we  are 
making  a  little  more  iron  with  10,000  Ib.  of  coke  than  we  intended. 
If  any  change  seems  necessary  it  is  then  well  to  reduce  the  weight 
of  ore  A  to  10,000,  leaving  everyth  ng  else  the  same.  This  will 
lighten  the  burden  and  bring  the  calculated  lime,  alumina  and 
silica  even  closer  to  the  desired  figures. 

Phosphorus  and  Manganese.  —  No  account  of  the  phosphorus 
has  been  taken  in  the  calculation  above.  This  is  necessary  some- 


50  THE   METALLURGY  OF   IRON   AND   STEEL 

times.  For  example,  if  ore  A  happened  to  be  very  high  in  phos- 
phorus we  could  not  use  so  large  a  proportion  of  it.  It  would  then 
be  necessary  either  to  secure  another  ore  low  in  both  phosphorus 
and  alumina,  or  else  to  make  a  slag  with  less  alumina.  The  same 
line  of  reasoning  applies  to  manganese. 


III 

THE  PURIFICATION  OF  PIG  IRON 

THE  large  amount  of  carbon  in  pig  iron  makes  it  both  weak  and 
brittle,  so  that  it  is  unfit  for  most  engineering  purposes.  It  is  used 
for  castings  that  are  to  be  subjected  only  to  compression,  or  trans- 
verse or  very  slight  tensile  strains,  as,  for  example,  supporting 
columns,  engine  bed-plates,  railroad  car  wheels,  water  mains,  etc., 
but  the  relatively  increasing  amount  of  steel  used  shows  the  prefer- 
ence of  engineers  for  the  stronger  and  more  ductile  material. 
To-day  three-fourths  of  the  pig  iron  made  in  the  United  States  is 
subsequently  purified  by  either  the  Bessemer,  open-hearth,  or 
puddling  process.  Each  of  these  will  reduce  the  carbon  to  any 
desired  point,  while  the  silicon  and  manganese  are  eliminated  as  a 
necessary  accompaniment  of  the  reactions,  —  indeed,  we  might 
almost  say  as  a  condition  precedent  to  carbon  reduction.  Phos- 
phorus and  sulphur  are  reduced  by  the  puddling  process,  and  by 
a  special  form  of  open-hearth  process  known  as  'the  basic  open- 
hearth  process.'1  The  complete  scheme  of  American  iron  and 
steel  manufacture  is  given  in  Fig.  29. 

Explanation  of  Fig.  29.  —  Practically  all  the  iron  ore  mined  is 
smelted  in  about  325  blast  furnaces,  producing  annually  25,000,000 
tons  of  pig  iron.  About  3  per  cent.2  of  this  pig  iron  is  remelted 
and  made  into  malleable  cast  iron;  20  per  cent,  is  remelted  and  cast 
as  gray  cast  iron;  52  per  cent,  is  purified  in  62  Bessemer  converters 
to  Bessemer  steel;  20  per  cent,  is  purified  in  465  basic  open-hearth 
furnaces;  2  per  cent,  is  purified  in  195  acid  open-hearth  furnaces, 
while  the  remaining  3  per  cent,  is  purified  in  3000  puddling  fur- 
naces to  make  wrought  iron.  The  wrought  iron  may  be  used  as 
such  for  pipe,  blacksmith  work,  small  structural  shapes,  etc.,  and 

1  The  basic  Bessemer  process  is  not  in  operation  in  America. 

2  The  numbers  and  percentages  given  in  this  figure  will  change  slightly 
from  time  to  time,  but  this  will  convey  to  a  beginner  an  idea  of  the  relative 
amounts  of  the  different  products  made. 

51 


52 


THE  METALLURGY  OF   IRON  AND   STEEL 


95  per  cent,  of  it  is  so  used;  the  other  5  per  cent,  is  remelted  in 
crucibles  to  make  crucible  steel.  To  sum  up,  about  23  per  cent, 
of  the  pig  iron  made  is  used  without  purification/  and  77  per  cent, 
is  purified  and  converted  into  another  form.  In  all  cases  of  purifi- 
cation the  impurities  are  removed  by  oxidizing  them;  and  we  must 


Skeleton  of  American  Iron  and  Steel  Manufacture 
1903 

50,032,279  Tons  of  Iron  Ore 


25,307,192  Tons  of  Pig  Iron 


62 

Bessemer 
.Converters 


Bessemer  Steel      Basic  Open- 
(12,275,250 )         Hearth  Steel 
(9,649,400; 


Acid  Open- 

Hearth  Steel 

(1,321,613; 


Wrought  Iron 


Used 
as  Such 


Crucible  Steel 
(118,000) 


All  Tons  are  2,240  Ibs.  each 


FIG.  29. 

again  emphasize  the  rule  that  unoxidized  elements  dissolve  in  the 
metal,  while  those  in  the  oxidized  condition  pass  into  the  slag,  or,, 
if  there  is  no  slag,  form  a  slag  for  and  of  themselves.  In  consider- 
ing the  Bessemer,  open-hearth,  and  puddling  processes  then,  we 
have  to  do  with  oxidizing  conditions,  \vhereas  the  opposite  was  the 

1  It  is  true  that  the  annealing  process  for  malleable  cast  iron  purifies  the 
outer  layers  of  the  castings  from  carbon,  and,  if  the  castings  are  very  thin, 
this  purification  may  extend  to  the  center;  but  this  is  not  primarily  a  purifi- 
cation process  and  will  be  treated  at  length  in  another  section. 


THE  PURIFICATION   OF   PIG   IRON 


53 


case  in  the  blast  furnace.  The  oxidation  is  effected  by  means  of 
the  oxygen  of  the  air  or  that  of  iron  ore,  Fe2O3,  or  its  equivalent, 
or  of  both  air  and  oxide  of  iron. 

There  is  not  an  exact  relation  between  the  amounts  of  pig  iron 
used  for  the  different  purposes  and  the  amounts  of  the  resulting 
materials.  In  1906  the  following  production  was  made: 

PRODUCTION   FOR    1906 


Cast  Iron  Used 

Made 

Malleable  cast  iron 

600,000*  tor 
5,100,000       ' 
13,150,000       ' 
5,150,000       ' 
500,000       ' 
800,000       ' 

(B 

750,000*  to] 
6,000,000 
12,275,250 
9,649,400 
1,321,613 
2,000^000* 
118,000 

is 

Gray  cast  iron                                       .... 

Bessemer  steel                             

Basic  open-hearth  steel           

Acid  open-hearth  steel  
Wrought  iron                          

Crucible  steel                      

*  Estimated. 

The  reason  for  the  discrepancy  is  found  in  the  scrap  iron  or 
steel  mixed  with  the  pig  iron  in  the  manufacture  of  gray-iron  cast- 
ings and  open-hearth  steel.  Perhaps  an  average  of  25  per  cent, 
of  old  scrap  will  be  mixed  with  75  per  cent,  of  new  pig  iron  for 
making  iron  castings,  and  50  per  cent,  or  so  of  steel  scrap  will  be 
mixed  with  50  per  cent,  or  so  of  pig  iron  in  the  open-hearth  proc- 
ess, while  wrought  iron  is  often  made  by  the  piling  and  rerolling 
of  old  wrought-iron  scrap. 

Bessemer  Process.  —  In  the  Bessemer  process,  perhaps  10  tons 
of  melted  pig  iron  is  poured  into  a  hollow  pear-shaped  converter 
lined  with  silicious  material.  Through  the  molten  material  is  then 
forced  25,000  cu.  ft.  of  cold  air  per  minute.  In  about  four  minutes 
the  silicon  and  manganese  are  all  oxidized  by  the  oxygen  of  the  air 
and  have  formed  a  slag.  The  carbon  then  begins  to  oxidize  to 
carbon  monoxide,  CO,  and  this  boils  up  through  the  metal  and 
pours  out  of  the  mouth  of  the  vessel  in  a  long  brilliant  flame.  After* 
another  six  minutes  the  flame  shortens  or  'drops';  the  operator 
knows  that  the  carbon  has  been  eliminated  to  the  lowest  practi- 
cable limit  (say  0.04  per  cent.)  and  the  operation  is  stopped.  So 
great  has  been  the  heat  evolved  by  the  oxidation  of  the  impurities 
that  the  temperature  is  now  higher  than  it  was  at  the  start, 
and  we  have  a  white-hot  liquid  mass  of  relatively  pure  metal. 
To  this  is  added  a  carefully  calculated  amount  of  carbon  to 


54 


THE  METALLURGY  OF  IRON  AND   STEEL 


produce  the  desired  degree  of  strength  or  hardness,  or  both; 
also  about  1.5  per  cent,  of  manganese  and  0.2  per  cent,  of  silicon.1 
The  manganese  is  added  to  remove  from  the  bath  the  oxygen  with 
which  it  has  become  charged  during  the  operation  and  which  would 
render  the  steel  unfit  for  use.  The  silicon  is  added  to  get  rid  of  the 


FIG.  30.  —  SECTION  THROUGH  BESSEMER  CONVERTER  WHILE  BLOWING. 

gases  which  are  contained  in  the  bath.  After  adding  these  ma- 
terials, or  '  recarburizing/  as  it  is  called,  the  metal  is  poured  into 
ingots,  which  are  allowed  to  solidify  and  then  rolled,  while  hot, 
into  the  desired  size  and  form.  The  characteristics  of  the  Besse- 
mer process  are:  (a)  Great  rapidity  of  purification  (say  ten  min- 
utes per  'heat');  (6)  no  extraneous  fuel  is  used;  and  (c)  the  metal 
is  not  melted  in  the  furnace  where  the  purification  takes  place. 
1  In  the  case  of  making  rail  steel. 


THE   PURIFICATION   OF   PIG   IRON 


55 


Acid  Open-hearth  Process.  —  The  acid  open-hearth  furnace  is 
heated  by  burning  within  it  gas  and  air,  each  of  which  has  been 
highly  preheated  before  it  enters  the  combustion  chamber.  A 
section  of  the  furnace  is  shown  in  Fig.  32.  The  metal  lies  in  a 
shallow  pool  on  the  long  hearth,  composed  of  silicious  material, 
and  is  heated  by  radiation  from  the  intense  flame  produced  as 
described.  The  impurities  are  oxidized  by  an  excess  of  oxygen  in 
the  furnace  gases  over  that  necessary  to  burn  the  gas.  This  action 
is  so  slow,  however,  that  the  3  to  4  per  cent,  of  carbon  in  the  pig 


rw 


& 


— (ff*  •' , 


FIG.  31.  —  BLOWHOLES  OR  GAS-BUBBLES  IN  STEEL. 

iron  takes  a  long  time  for  combustion.  The  operation  is  therefore 
hastened  in  two  ways :  (a)  iron  ore  is  added  to  the  bath  to  produce 
the  reaction 

Fe2O3  -f  3C=  SCO  -f  2Fe, 

and  (6)  the  carbon  is  diluted  by  adding  varying  amounts  of  cold 
steel  scrap.  The  steel  scrap  is  added  to  the  furnace  charge  at 
the  beginning  of  the  process,  and  it  takes  about  6  to  10  hours  to 
purify  a  charge,  after  which  we  recarburize  and  cast  the  metal 
into  ingots.  The  characteristics  of  the  open-hearth  process  are: 
(a)  A  long  time  occupied  in  purification;  (6)  large  charges  are 
treated  in  the  furnace  (the  modern  practice  is  usually  30  to  70 
tons  to  a  furnace) ;  (c)  at  least  a  part  of  the  charge  is  melted  in  the 


56 


THE  METALLURGY   OF   IRON   AND   STEEL 


purification  furnace;  and  (d)  the  furnace  is  heated  with  preheated 
gas  and  air. 

Basic  Open-Hearth  Process.  —  The  basic  open-hearth  opera- 
tion is  similar  to  the  acid  open-hearth  process,  with  the  difference 


FIG.    32.  —  DIAGRAM    OF  REGENERATIVE  OPEN-HEARTH  FURNACE. 

The  four  chambers  below  this  furnace  are  filled  with  checkerwork  of  brick  with  hori- 
zontal and  vertical  channels  through  which  the  gas  and  air  may  pass.  The  gas  enters  the 
furnace  through  the  inner  regenerative  chamber  on  one  side  and  the  air  enters  through 
the  corresponding  outer  one.  They  meet  and  unite,  passing  through  the  furnace  and 
thence  dividing  into  proportional  parts  and  passing  to  the  chimney  through  the  two  regen- 
erative chambers  at  the  opposite  end.  In  this  way  the  brickwork  in  the  chambers  is  heated 
up  by  the  waste  heat  of  the  furnace.  The  current  of  gas,  air,  and  products  of  combustion 
is  changed  every  twenty  minutes  whereby  all  four  regenerators  are  always  kept  hot.  The 
gas  and  air  enter  in  a  highly  preheated  condition  and  thus  give  a  greater  temperature  of 
combustion,  while  the  products  of  combustion  go  out  to  the  chimney  at  a  relatively  low 
heat  and  thus  fuel  economy  is  promoted. 


that  we  add  to  the  bath  a  sufficient  amount  of  lime  to  form  a  very 
basic  slag.  This  slag  will  dissolve  all  the  phosphorus  that  is  oxi- 
dized, which  an  acid  slag  will  not  do.  We  can  oxidize  the  phos- 


THE   PURIFICATION   OF   PIG  IRON 


57 


phorus  in  any  of  these  processes,  but  in  the  acid  Bessemer  and  the 
acid  open-hearth  furnaces  the  highly  silicious  slag  rejects  the 
phosphorus,  and  it  is  immediately  deoxidized  again  and  returns 
to  the  iron.  The  characteristics  of  the  basic  open-hearth  process 
are  the  same  as  those  of  the  acid  open-hearth,  with  the  addition 
of:  (e)  Lime  is  added  to  produce  a  basic  slag;  (/)  the  hearth  is 
lined  with  basic,  instead  of  silicious,  material  in  order  that  it  may 
not  be  eaten  away  by  this  slag;  and  (g)  impure  iron  and  scrap  may 
be  used,  because  phosphorus  and,  to  a  limited  extent,  sulphur 
can  be  removed  in  the  operation. 

Puddling  Process.  —  Almost  all  the  wrought  iron  to-day  is 
made  by  the  puddling  process,  invented  by  Henry  Cort  about 
1780,  with  certain  valuable  improvements  made  by  Joseph  Hall 
fifty  years  later.  In  this  process  the  pig  iron  is  melted  on  the 
hearth  of  a  reverberatory  furnace  lined  with  oxide  of  iron.  During 


FIG.  33.  —  PUDDLING  FURNACE. 

the  melting  there  is  an  elimination  of  silicon  and  manganese  and 
the  formation  of  a  slag  which  automatically  adjusts  itself  to  a  very 
high  content  of  iron  oxide  by  dissolving  it  from  the  lining.  After 
melting,  the  heat  is  reduced  and  a  reaction  set  up  between  the 
iron  oxide  of  the  slag  and  the  silicon,  manganese,  carbon,  phos- 
phorus and  sulphur  of  the  bath,  whereby  the  impurities  are  oxi- 
dized and  all  removed  to  a  greater  or  less  extent.  The  slag,  be- 
cause of  its  basicity  (by  iron  oxide),  will  retain  all  the  phosphorus 
oxidized,  and  therefore  the  greater  part  of  this  element  is  removed. 
The  oxidation  of  all  the  impurities  is  produced  chiefly  by  the  iron 


58 


THE  METALLURGY  OF   IRON  AND   STEEL 


oxide  in  the  slag  and  the  lining  of  the  furnace,  although  it  is 
probable  that  excess  oxygen  in  the  furnace  gases  assists,  the  slag 
acting  as  a  carrier  of  oxygen  from  it  to  the  impurities. 

The  purification  finally  reaches  that  stage  at  which  the  utmost 
heat  of  the  furnace  is  not  sufficient  to  keep  the  charge  molten, 
because  iron,  like  almost  every  other  metal,  melts  at  a  higher  tem- 
perature the  purer  it  is.  The  metal  therefore  l  comes  to  nature/ 
as  it  is  called,  that  is  to  say,  it  assumes  a  pasty  state.  The  iron 
is  rolled  up  into  several  balls,  weighing  125  to  180  Ib.  apiece, 
which  are  removed  from  the  furnace,  dripping  with  slag,  and  car- 
ried over  to  an  apparatus,  where  they  are  squeezed  into  a  much 
smaller  size  and  a  large  amount  of  slag  separated  from  them. 
The  squeezed  ball  is  then  rolled  between  grooved  rolls  to  a  bar, 
whereby  the  slag  is  still  further  reduced,  so  that  the  bar  contains 
at  the  end  usually  about  1  or  2  per  cent.  This  puddled  bar,  or 
'muck  bar/  is  cut  into  strips  and  piled 'up,  as  shown  in  Fig.  34, 


FIG.  34.  —  METHOD  OF  PILING  MUCK  BAR. 

into  a  bundle  of  bars  which  are  bound  together  by  wire,  raised  to  a 
welding  heat,  and  again  rolled  into  a  smaller  size.  This  rolled 
material  is  then  known  as  '  merchant  bar/  and  all  wrought  iron, 
except  that  which  is  to  be  used  for  manufacture  into  crucible  steel, 
is  treated  in  this  way  before  sale.  The  effect  of  the  further  rolling 
is  to  eject  more  slag,  and  also  to  make  a  cross  network  of  fibers, 
instead  of  a  line  of  fibers  all  running  in  the  same  direction,  i.e., 
lengthwise  of  the  bar.  The  fibers  are  produced  by  the  action  in 
rolling  of  drawing  out  the  slag  into  strings,  long  fibers  of  metal 
also  being  produced,  each  of  which  is  surrounded  by  an  envelope 
of  slag. 


THE   PURIFICATION   OF   PIG   IRON  59 


COMPARISON  OF  PURIFICATION  PROCESSES 

Acid  with  Basic  Open-Hearth.  — Acid  open-hearth  steel  is  be- 
lieved by  engineers  to  be  better  than  basic,  and  is  usually  specified 
for  in  all  important  parts  of  structures,  although  not  so  rigidly 
to-day  as  a  few  years  ago.  This  is  in  spite  of  the  fact  that  phos- 
phorus and  sulphur,  two  very  harmful  elements,  are  lower  in  the 
basic  steel.  The  basic  process  is  much  less  expensive  than  the 
acid,  because  high  phosphorus  pig  iron  and  scrap  are  cheap,  and 
the  lower  cost  of  materials  used  more  than  balances  the  greater 
cost  of  the  basic  lining  and  the  lime  additions  and  the  circumstance 
that  the  acid  furnace  has  a  higher  output  because  the  heats  are 
shorter.  The  reasons  for  the  preference  of  acid  steel  are  as  follows : 

(a)  A  basic  slag  will  dissolve  silicon  from  the  metal;  we  there- 
fore recarburize  in  the  basic  process  by  adding  the  recarburizer  to 
the  steel  after  it  has  left  the  furnace,  instead  of  in  the  furnace,  as 
we  do  in  the  acid  process.     Should  any  basic  slag  be  carried  over 
with  the  metal,  however,  which  is  liable  to  happen,  there  is  the 
danger  that  the  ingots  will  be  too  low  in  silicon.     They  are  then 
impregnated  with  gas  bubbles,  or  'blow  holes/ 

(b)  Moreover,  the  recarburizer  does  not  mix  with  the  steel  as 
well  if  it  is  not  added  in  the  furnace,  and  this  sometimes  produces 
irregularities. 

(c)  A  basic  slag  is  usually  more  highly  oxidized  than  an  acid 
one ;  therefore  the  metal  at  the  end  of  the  operation  is  more  highly 
charged  with  oxygen.     For  this  reason  we  add  a  larger  amount  of 
manganese  in  the  recarburizer,  but  the  remedy  is  never  quite  as 
good  as  prevention. 

(d)  Since  we  cannot  remove  the  phosphorus  from  the  bath  in 
the  acid  process,  it  is  necessary  to  use  only  picked  iron  and  scrap, 
whereas,  in  the  basic  process,  good  steel  can  be  made  from  almost 
any  quality  of  material.     Many  engineers  believe,  however,  that  a 
better  grade  of  steel  results  from  using  the  picked  material. 

(e)  It  occasionally  happens  in  the  basic  process  that,  after  the 
phosphorus  has  all  been  oxidized  in  the  slag  and  the  operation  is 
ended,  some  of  it  will  get  back  into  the  metal  again.     This  is 
especially  liable  to  happen  when  basic  slag  is  carried  over  into  the 
ladle  before  the  recarburizer  is.all  in.     If  this  occurs,  and  if  the  bath 
is  very  hot,  a  reaction  may  take  place  between  the  basic  slag  and 


60  THE  METALLURGY  OF   IRON  AND   STEEL 

the  acid  lining  of  the  ladle.     In  this  way  the  slag  will  be  enriched 
in  silica  and  phosphorus  will  be  forced  out  of  it. 

Basic  Open-Hearth  with  Bessemer.  —  Basic  open-hearth  steel 
is  better  than  Bessemer  steel.  The  reasons  for  this  are  believed 
to  be: 

(a)  The  open-hearth  process  being  slower,  more  attention  and 
care  can  be  given  to  each  detail.     This  is  particularly  true  of  the 
ending  of  the  process,  for  if  the  Bessemer  process  is  continued  only 
a  second  or  so  too  long,  the  bath  is  highly  charged  with  oxygen, 
to  its  detriment,  and  even  under  normal  circumstances  there  is 
more  oxygen  in  the  metal  at  the  end  of  the  Bessemer  process  than 
at  the  end  of  the  basic  open-hearth,  because  there  has  been  so 
intimate  a  mixture  between  metal  and  air. 

(b)  For  the  same  reason  the  Bessemer  metal  is  believed  to  con- 
tain more  nitrogen  and  hydrogen,1  which  are  thought  to  be  dele- 
terious. 

(c)  The  Heat  of  the  Bessemer  process  is  dependent  upon  the  im- 
purities in  the  pig  iron,  and  especially  upon  the  amount  of  the 
silicon,  and  can  be  controlled  only  to  a  limited  extent  by  methods 
that  are  not  perfect  in  their  operation.     Furthermore,  the  heat  is 
regulated  according  to  the  judgment  of  the  operator  and  his  skill 
in  estimating  the  temperature  of  the  flame.     Irregularities  there- 
fore result  at  times,  and  these  produce  an  effect  on  the  steel,  be- 
cause the  temperature  at  which  the  ingots  are  cast  should  be 
neither  too  high  nor  too  low.     It  is  true  that  the  temperature  of  the 
open-hearth  steel  is  also  regulated  by  the  judgment  of  the  operator, 
but  more  time  is  afforded  for  exercising  this  judgment  and  for 
controlling  the  heat. 

(d)  In  the  Bessemer  process  we  must  get  rid  of  all  the  carbon 
first  and  then  recarburize  to  the  desired  point.     In  the  open-hearth 
process  we  may  stop  the  operation  at  any  desired  amount  of  carbon, 
and  then  recarburize  only  a  small  amount.     Therefore  the  open- 
hearth  has  the  advantage  of  greater  homogeneity  when  making 
high-carbon  steel,  since  a  very  large  amount  of  recarburizer  may 
not  distribute  itself  uniformly. 

(e)  In  order  to  produce  the  best  quality  of  steel,  it  must  be  cast 
into  ingot  molds  within  a  certain  limited  range  of  temperature, 
which  varies  according  to  the  amount  of  carbon,  etc.,  that  it  con- 
tains.    Therefore,  in  casting  the  very  large  heats  of  the  open- 

1  From  moisture  in  the  blast. 


THE   PURIFICATION   OF   PIG   IRON  61 

hearth  process,  the  ingots  must  be  very  large,  else  the  first  one  will 
be  too  hot  and  the  last  one  too  cold  for  the  best  results.  On  the 
other  hand,  if  the  ingots  are  large,  segregation  is  liable  to  be  ex- 
cessive (see  page  180). 

For  nearly  fifteen  years  the  Bessemer  process  has  been  fighting 
a  losing  battle  to  maintain  its  supremacy  against  the  inroads  of 
the  basic  open-hearth,  which  have  been  possible  because  of  the 
increasing  cost  of  Bessemer  pig  iron,  due  to  the  exhaustion  of  the 
low  phosphorus  ores.  The  pig  iron  for  the  Bessemer  process  must 
contain  so  little  phosphorus  that,  after  allowing  10  per  cent,  loss  of 
metal  during  the  blow,  the  phosphorus  in  the  steel  shall  be  not 
over  0.100  per  cent.  Ores  low  enough  in  phosphorus  to  make 
this  grade  of  metal  have,  therefore,  come  to  be  known  as  '  Besse- 
mer ores/  The  requirement  of  such  an  ore  is  that  the  per- 
centage of  iron  in  it  must  be  1000  times  the  percentage  of  phos- 
phorus. During  the  year  1906,  the  Bessemer  process  in  the  United 
States  yielded  very  much  to  the  basic  open-hearth,  and  it  would 
seem  as  if  there  was  no  chance  of  its  ever  taking  up  so  impor- 
tant a  position  again  unless  new  iron  ores  low  in  phosphorus  are 
discovered. 

On  account  of  its  ability  to  make  low  carbon  steel  more  readily 
than  the  basic  open-hearth,  the  Bessemer  process  has  a  firm  hold 
on  the  wire  and  welded  steel-pipe  industry,  although  even  here  the 
open-hearth  process  has  encroached.  For  rolling  very  thin  for 
tinplate,  etc.,  we  want  a  metal  relatively  high  in  phosphorus,  and 
therefore  the  Bessemer  process  is  largely  used  here,  although  in 
some  cases  ferrophosphorus  is  being  added  to  basic  open-hearth 
metal  to  accomplish  the  same  result.  The  reason  phosphorus  is 
desired  is  because  the  plates  are  rolled  very  thin  by  doubling 
them  up  and  putting  several  thicknesses  through  the  rolls  at  the 
same  time.  Low  phosphorus  metal  welds  together  too  much 
under  these  circumstances. 

The  chief  requisites  of  railroad  rails  are  lack  of  brittieness  and 
ability  to  withstand  wear.  The  Bessemer  process  is  able  to  pro- 
vide such  a  material,  and  it  works  so  well  in  conjunction  with  the 
rapid,  continuous  operation  of  the  rail-rolling  mill  that  it  has  a 
decided  advantage.  It  produces  a  small  tonnage  of  ingots  at 
frequent  intervals  (say  15  tons  every  7  minutes),  while  the  open- 
hearth  process  provides  a  large  tonnage  of  ingots,  which  may  come 
at  irregular  intervals  and  thus  alternately  delay  and  overcrowd 


62 


THE  METALLURGY  OF  IRON  AND  STEEL 


the  rail-mill  operations.  But  notwithstanding  these  advantages, 
an  increasing  tonnage  of  basic  open-hearth  rails  is  made  every  year 
in  the  United  States. 

During  1907  this  phase  of  the  industry  has  attracted  wide- 
spread interest,  owing  to  reports  of  an  alarming  number  of  rail 
breakages  and  of  the  action  of  some  railroads  in  blaming  the 
Bessemer  process  therefor.  It  is  true  that  every  year  there  is  a 
greater  scarcity  of  Bessemer  ores  and  therefore  an  increasing 
amount  of  phosphorus  in  the  steel  manufactured,  so  that  it  is  no 
secret  that  many  rails  have  been  made  within  the  past  year 
containing  more  than  the  allowable  0.1  per  cent,  phosphorus. 
Phosphorus  makes  the  steel  brittle,  especially  under  shock  and 
in  cold  weather.  It  also  makes  the  steel  hard  and  more  able  to 
resist  wear;  but  this  hardness  is  better  obtained  by  means  of 
carbon,  and  low-phosphorus,  high-carbon  steel  rails  would  un- 
doubtedly break  less  often  in  the  track.  It  is  to  be  remembered 
that  heavier  trains  are  being  run  every  year,  and  that  this  brings 
greater  strains  upon  the  rails,  to  meet  which  they  have  not  been 
correspondingly  increased  in  size.  At  the  present  time  such  a 
very  large  amount  of  capital  is  tied  up  in  Bessemer-rail  mills,  and 
it  would  take  so  long  to  change  them  over  into  open-hearth 
mills,  that  there  is  no  immediate  liability  of  a  great  replacement. 
The  acid-  and  basic-steel  production  of  the  principal  countries 
of  the  world  is  shown  in  Tables  IX  and  X,  while  the  recent 
history  of  open-hearth  steel-rail  manufacture  is  shown  briefly  in 
Table  VIII. 

TABLE   VIIL— AMERICAN  RAILROAD  RAIL  MANUFACTURE 


Bessemer  J 
Gross  Tons 

Open-Hearth  2 
Gross  Tons 

Wrought  Iron3 
Gross  Tons 

Total 
Gross  Tons 

1900 

2  383  654 

1  333 

695 

2  385  682 

1901          .    . 

2  870  816 

2093 

1  730 

2  874  639 

1902 

2  935  392 

6029 

6  512 

2  947  933 

1903      

2  946  756 

45054 

667 

2  992  477 

1904  

2  137  957 

145  883 

871 

2  284  711 

1905  

3,188,675 

183  264 

318 

3  372  257 

1906  

3  700  000* 

250  000* 

*  Estimated. 

1  The  first  Bessemer  rails  were  made  commercially  in  1867. 

2  In  1881,   22,515  gross  tons  of  open-hearth  rails  were  produced.     The 
first  open-hearth  rails  were  made  in  1878. 

3  The  maximum  production  of  iron  rails  was  808,866  gross  tons  in  1872. 


THE  PURIFICATION   OF   PIG   IRON  63 

TABLE  IX.— STEEL  PRODUCTION  OF  PRINCIPAL  COUNTRIES:  1906 


United  States 

Germany 

Great  Britain 

Acid  converter 

12,275,253 

407,688 

1,307,149 

Basic  converter 

6,772,804 

600,189 

Total  converter           

12,275,253 

7,180,492 

1,907,338 

Acid  open-hearth 

1  321  613 

230,668 

3,378,691 

Basic  open-hearth 

9  649  385 

3  534  612 

1  176  245 

Total  open-hearth          .  .  . 

10,970  998 

3,765,280 

4,554,936 

Crucible  and  special       

118,500 

189,313 

Total  

23,364,751 

11,135,085 

6,462,274 

Proportion  steel  to  pig  iron  

92.3 

89.2 

63.7 

TABLE  X.— MAKE  OF  ACID  AND  BASIC  STEEL:  1906 


ACID 

BASIC 

Tons 

Per  cent. 

Tons 

Per  cent. 

United  States 

13  715  366 

58  7 

9  649  385 

41  3 

Germany 

715  952 

6  4 

10  419  133 

93  6 

Great  Britain 

4  685  840 

72  5 

1  776  434 

27  5 

Total  

19  117  158 

46  7 

21  844  952 

53  3 

Crucible  Steel  with  Others.  —  Crucible  steel  is  the  most  expen- 
sive of  all  and  costs  at  least  three  times  as  much  as  the  next  in 
price  —  acid  open-hearth  steel.  It  is  also  the  best  quality  of  steel 
manufactured,  and  for  very  severe  service,  such  as  the  points 
and  edges  of  cutting  tools,  the  highest  grades  of  springs,  armor- 
piercing  projectiles,  etc.,  it  should  always  be  employed.  The 
reason  for  its  superiority  is  believed  to  be  because  it  is  manufac- 
tured in  a  vessel  which  excludes  the  air  and  furnace  gases,  and  is 
therefore  freer  from  oxygen,  hydrogen  and  nitrogen.  Perhaps 
the  fact  that  the  process  is  in  some  ways  under  a  little  better  con- 
trol than  any  of  the  others,  and  receives  more  care,  on  account  of 
being  manufactured  in  small  units,  assists  in  raising  its  grade. 
Crucible  steels  are  usually  higher  in  carbon  than  Bessemer  and 
open-hearth  steels,  because  the  special  service  to  which  the  cru- 
cible steels  are  adapted  is  usually  one  requiring  steel  that  can 
be  hardened  and  tempered  —  for  example,  cutting  tools,  springs, 
etc.,  and  only  the  high-carbon  steels  are  capable  of  this  hardening 
and  tempering. 


64  THE  METALLURGY  OF   IRON  AND   STEEL 

Wrought  Iron  with  Low-Carbon  Steel.  —  Wrought  iron  costs  from 
10  to  20  per  cent,  more  than  the  cheapest  steel.  Its  claim  to  superi- 
ority over  dead-soft  steel  consists  in  its  purity  and  the  presence  in 
it  of  slag.  Just  how  much  advantage  the  slag  is  has  never  been 
proven;  it  gives  the  metal  a  fibrous  structure  which,  perhaps,  in- 
creases its  toughness  and  its  resistance  to  breaking  under  bending 
or  under  a  sudden  blow  or  shock.  Some  think  that  the  slag  also 
assists  in  the  welding  of  the  material,  but  this  is  doubtful,  and  it  is 
probable  that  the  easy  weldability  of  wrought  iron  is  due  alone 
to  its  being  low  in  carbon.  Some  also  believe  that  the  slag  assists 
the  metal  in  resisting  corrosion ;  hence  one  reason  for  the  preference 
of  engineers  for  wrought-iron  pipe  for  boilers  and  other  purposes. 
There  are  other  qualities  of  wrought  iron  which  may  tend  to  make 
it  corrode  less  than  steel,  chief  among  which  are  the  absence  of 
blowholes  and  possibly  the  absence  of  manganese,  and  the  pres- 
ence of  phosphorus.  It  is  now  believed  by  many  that  manganese 
starts  an  electrolytic  action  which  hastens  corrosion.  An  ad- 
vantage of  wrought  iron  in  this  connection  is  its  rough  surface  to 
which  paint  or  other  protective  coatings  will  adhere  more  firmly 
than  to  the  comparatively  smooth  surface  of  steel.  Nevertheless 
the  evidence  goes  to  show  that  properly  made  steel  corrodes  no 
more  than  wrought  iron,  especially  in  boilers,  pipe,  and  other 
articles  which  cannot  be  coated. 

The  properties  of  wrought  iron  are  the  nearest  to  those  of  pure 
iron  of  any  commercial  material,  notwithstanding  its  slag.  This 
is  because  the  slag  is  mechanically  mingled  with  the  metal  and 
does  not  interfere  with  its  chemical  or  physical  actions.  There- 
fore wrought  iron  is  greatly  preferred  for  electrical  conductivity 
purposes  and  as  a  metal  with  high  magnetic  power,  for  armatures 
of  electromagnets,  etc. 

The  advantages  I  have  mentioned,  the  conservatism  of  engi- 
neers, and  the  capital  previously  invested  in  puddling  furnaces 
are  the  chief  factors  in  keeping  alive  the  manufacture  of  wrought 
iron.  It  was  freely  predicted  that  the  invention  of  the  Bessemer 
and  open-hearth  processes  would  bring  about  the  extinction  of 
the  puddling  process,  but  these  prophecies  have  never  been  ful- 
filled, although  the  importance  of  wrought  iron  has  waned  very 
greatly  in  fifty  years.  When  under  strain  greater  than  it  can 
withstand  wrought  iron  stretches  more  uniformly  over  its'  entire 
length  than  steel,  as  shown  by  the  following  tests: 


THE   PURIFICATION   OF   PIG   IRON 


65 


STRAIN  TESTS  ON  WROUGHT  IRON 


Elastic  Limit 

Ultimate 
Strength 

Elongation 
per  cent. 

Reduc- 
tion of 
Area 

Per  cent. 
28.30 
51\50 

Wrought  iron  . 
Steel  

Lb.  per  sq.  in. 

31,550 
33,150 

Lb.  per  sq.  in. 
48,810 
59,260 

In  12  in. 
23 
39 

In  18  ft. 
15.22 
14.40 

Summary.  —  In  order  of  expense  and  of  quality  the  different 
steels  are  arranged  as  follows:  (1)  Crucible,  (2)  acid  open-hearth, 
(3)  basic  open-hearth,  and  (4)  Bessemer.  The  amounts  of  the  dif- 
ferent kinds  made  in  America  to-day  and  ten  years  ago  are  shown  in 
Table  XI.  Though  I  have  not  made  a  direct  comparison  between 
certain  of  the  classes,  e.g.,  acid  open-hearth  with  Bessemer,  their 
relations  may  be  easily  learned  by  collating  the  other  comparisons 
given. 

TABLE  XI 


1906.. 
1896.. 


Bessemer 

12,275,253     52% 
4,909,128     78% 


Open-Hearth 
9,649,385     41% 
776,256     12% 


1,321,613 
522,444 


6% 
9% 


Crucible,  etc. 
118,500      1% 
68,524     1% 


Many  engineers  will  be  interested  in  the  uses  to  which  the 
annual  steel  and  wrought  iron  production  of  the  United  States 
is  put,  which  are  shown  below: 

TABLE  XII.— USES  OF  STEEL    AND  WROUGHT  IRON.     1906. 


GROSS  TONS,  1906 

Steel,  tons 

Wrought 
Iron,  tons 

Railroad  rails                              

3  977  872 

15 

Railroad  rail  splice  bars                    

213  977 

10,934 

Plates  and  sheets                    

4  107  783 

74,373 

Structural  shapes                        

2  114053 

4,719 

Merchant  bars*                                   

2  510  852 

1  481,348 

Rods  for  wire  and  wire  products 

1  310  413 

1,201 

Rods  for  wire  nails 

560  000§ 

Plate  for  cut  nails 

37032 

17  179 

Skelpf 

1  137  068 

391  517 

Hoops,  bands  and  cotton  ties 

579018 

1  332 

Blooms  and  billetsj 

205  648 

462 

All  other  rolled  shapes 

648  195 

203  477 

Castings     

700  000  § 

Totals  

18  101  911 

2  186  557 

*  Merchant  bars  are  small  bars  to  be  worked  up  into  other  forms. 
t  Skelp  is  welded  into  pipe. 

t  Blooms  and  billets  are  larger  pieces  to  be  worked  up  farther. 
$  Estimated. 


66  THE    METALLURGY  OF   IRON   AND   STEEL 

DISTINGUISHING  BETWEEN  THE  DIFFERENT  PRODUCTS 

Low-carbon  steel  pipe,  merchant  bars,  horseshoe  blanks, 
etc.,  sometimes  masquerade  under  the  name  of  wrought-iron ; 
high-carbon  open-hearth  and  Bessemer-steel  merchant  bars, 
tool  blanks,  etc.,  sometimes  masquerade  as  'crucible  steel/  or 
perhaps  'cast  steel/  which  is  the  trade  name  for  crucible  steel; 
other  deceptions  are  not  unknown;  indeed,  even  malleable  cast 
iron  is  sold  oftentimes  as  'steel  castings.'  It  is  therefore  im- 
portant for  engineers  to  understand  the  essential  differences 
between  these  materials,  although  care  in  the  wording  of  contracts 
and  specifications  should  be  the  important  consideration  and 
should  precede  watchfulness  over  the  products.  The  definitions 
of  iron  and  steel  materials  are  in  such  a  confused  and  unsettled 
condition  that  it  does  not  do  to  rely  upon  them  at  all,  especially 
where  a  lawsuit  may  be  involved;  and  contracts  in  clear,  simple 
language,  free  from  legal  and  metallurgical  phraseology,  are  the 
best  safeguards.  But  even  where  it  is  entirely  plain  what  material 
is  called  for,  there  is  always  a  temptation  to  substitute  steel  for 
wrought  iron,  Bessemer  for  open-hearth,  basic  for  acid,  and 
Bessemer  or  open-hearth  for  crucible,  steel.  In  case  one  such 
substitution  is  suspected,  there  are  means  by  which  the  material 
may  be  tested,  aside  from  its  strength  and  ductility,  which  may 
or  may  not  be  in  the  contract.  The  tests  are  somewhat  delicate 
and  usually  require  the  judgment  and  experience  of  an  expert— 
one  who  has  standard  samples  of  the  different  grades  of  material 
for  comparison,  because  the  details  of  manufacture  vary  from 
district  to  district,  and  still  more  so  with  the  purposes  for  which 
the  products  are  to  be  used. 

Wrought  iron  may  be  distinguished  from  low-carbon  'steel 
by  the  fact  that  it  contains  slag.  Usually,  there  is  more  than 
1  per  cent,  of  slag  in  iron  and  less  than  0.2  per  cent,  of  slag  (in- 
cluding metallic  oxides)  in  steel.  The  slag  may  be  determined 
either  by  chemical  or  microscopical  analysis.  Normal  wrought 
iron  is  practically  free  from  manganese,  while  normal  Bessemer 
and  open-hearth  steel  will  contain  0.5  per  cent,  or  more.  Wrought 
iron  generally  contains  more  than  0.1  per  cent,  phosphorus,  while 
good  steel  should  never  do  so. 

Crucible  steel  normally  has  less  than  0.4  per  cent,  manganese 
and  more  than  0.2  per  cent,  silicon,  while  open-hearth  and  Bessemer 


THE   PURIFICATION   OF   PIG   IRON  67 

steels  normally  have  more  than  0.4  per  cent,  manganese  and  less 
than  0.2  per  cent,  silicon.  In  the  case  of  steel  castings,  however, 
this  rule  for  silicon  does  not  apply,  as  Bessemer  and  open-hearth 
steel  castings  are  sometimes  as  high  as  0.6  per  cent,  in  silicon. 
It  is  possible  to  make  both  Bessemer  and  open-hearth  steels  low 
in  manganese,  but  they  cannot  be  made  low  in  both  manganese 
and  silicon  without  great  danger  from  blow-holes,  while  this 
difficulty  is  not  met  with  to  the  same  extent  in  crucible  steel. 
When  crucible  steel,  low  in  carbon,  is  ordered,  there  is  a  much 
greater  temptation  to  substitute  another  steel  for  it. 

Acid  open-hearth  steel  may  be  distinguished  from  basic  open- 
hearth  steel  by  its  being  normally  higher  in  silicon,  and  usually 
in  phosphorus  also,  but  lower  in  manganese.  The  same  differences 
exist  between  acid  and  basic  Bessemer  steel. 

Basic  open-hearth  steel  may  be  distinguished  from  Bessemer 
steel  by  its  lower  manganese,  silicon,  phosphorus  and  (generally) 
sulphur,  as  well  as  by  the  fact  that  it  dissolves  much  more  slowly 
in  dilute  hydrochloric  acid. 

It  is  possible  to  place  such  physical  specifications  in  a  contract 
as  to  practically  insure  obtaining  the  grade  of  material  ordered. 
For  example,  such  a  high  degree  of  ductility  may  be  demanded, 
especially  the  percentage  elongation  in  ten  or  twenty  feet,  that 
nothing  but  wrought  iron  will  give  it;  the  strength  and  ductility 
may  be  put  so  high  as  to  make  it  too  dangerous  to  try  to  supply 
anything  but  crucible  steel  for  the  order;  or  they  may  be  put  a 
little  lower  so  as  practically  to  preclude  Bessemer  steel.  The 
average  physical  difference  between  acid  and  basic  open-hearth 
steels  is  not  great  enough  to  make  this  method  of  assurance  so 
practicable,  but  it  is  possible  in  the  case  of  basic  and  acid  Bessemer 
steel  in  England,  where  alone  both  these  kinds  of  steel  are  made 
in  important  quantities. 

MISCELLANEOUS  PURIFICATION  PROCESSES 

Bell-Krupp  Process.  —  The  late  Sir  I.  Lowthian  Bell  devised  a 
process  in  which  liquid  pig  iron  is  violently  stirred  up  with  iron 
oxide,  producing  a  slag  which  carries  away  more  than  90  per  cent,  of 
the  silicon  and  phosphorus  in  the  metal  in  the  course  of  from  7  to  10 
minutes.  As  soon  as  carbon  begins  to  burn  the  process  is  stopped, 
and  therefore  there  is  almost  no  change  in  this  element.  The 


68  THE  METALLURGY  OF   IRON   AND   STEEL 

operation  is  conducted  on  the  revolving  hearth  of  a  mechanical 
puddling  furnace,  into  which  the  melted  iron  is  poured  while  the 
hearth  is  rotating  at  about  11  revolutions  per  minute.  The  tem- 
perature is  lower  than  that  of  the  open-hearth  process,  in  order 
that  the  elimination  of  phosphorus  may  be  rapid. 

The  purified  metal  is  used  to  some  extent  in  the  manufacture  of 
crucible  steel.  During  recent  years,  when  the  low  phosphorus 
ores  of  America  have  become  more  scarce  and  the  price  of  Besse- 
mer pig  iron  is  consequently  increased,  the  metal  has  been  bought 
to  a  limited  extent  by  foundry  men  using  the  acid  open-hearth 
process  or  the  baby  Bessemer  process  for  the  production  of  steel 
castings. 

Finery  Fire.  —  This  furnace  is  known  under  various  names, 
such  as  'refinery  hearth/  ' running-out  fire/  'finery  fire/  etc.  It 
consists  of  a  shallow,  rectangular  hearth,  surrounded  on  the  sides 
by  water-cooled,  hollow  blocks  of  iron  about  3  to  3J  ft.  long  by  2 
ft.  wide  and  24  to  30  in.  deep.  In  and  above  this  hearth  is  built  a 
fire  of  coke  upon  which  is  placed  500  or  600  Ib.  of  pig  iron.  The 
coke  is  burned  by  a  blast  at  2  to  3  Ib.  pressure  from  2  to  3  tuyeres 
on  each  side,  and  the  pig  iron  gradually  melts  and  sinks  below  it. 
When  this  takes  place,  more  coke  and  pig  iron  is  placed  upon  the 
top,  and  the  operation  repeated.  A  bath  of  pig  iron  forms  in  the 
hearth,  and  upon  this  the  blast  from  the  tuyeres  impinges.  This 
oxidizes  the  silicon  in  the  metal,  and  also  a  large  amount  of  iron, 
phosphorus,  and  sulphur.  A  slag  high  in  iron  oxide  and  therefore 
very  basic  is  formed.  As  the  temperature  is  low,  phosphorus  is 
eliminated  without  burning  much  carbon,  and  the  result  is  the 
production  of  a  purified  iron  still  high  in  the  latter  element. 

It  takes  about  two  hours  to  perform  this  purification,  and  then 
the  metal  is  tapped  out  from  the  tap-hole  in  the  front.  It  usually 
runs  into  the  long,  shallow  trough,  whence  the  name  'running-out 
fire';  but  sometimes  the  refined  metal  is  not  allowed  to  cool,  but  is 
run  directly  into  the  furnace  in  which  the  purification  is  to  be  com- 
pleted. The  consumption  of  coke  is  about  one-eighth  of  the  metal 
produced,  and  the  loss  from  5  to  20  per  cent.,  depending  upon 
the  purity  of  the  iron  treated. 

The  running-out  fire  is  frequently  used  in  connection  with  the 
charcoal  finery  known  as  the  'knobbling  fire/  to  produce  knobbled 
charcoal-iron,  which  is  employed  especially  for  boiler  tubes  and  to 
-a  less  extent  for  boiler-plate,  wire,  rivets,  etc.  Running-out  fires 


THE   PURIFICATION   OF   PIG   IRON 


69 


for  this  purpose  are  often  known  as  'melting  fineries/  because  in 
them  the  pig  iron  is  melted  before  it  goes  to  the  knobbling  fire. 
There  are  usually  two  tuyeres  in  the  back,  and  the  melted  metal, 
after  the  operation  described  just  above,  is  run  directly  into  two 
charcoal  fineries,  which  are  very  similar  in  construction  to  the 


FIG.  35.  —  MELTING  FINERY. 

melting  fineries,  but  have  only  one  tuyere,  situated  in  the  back, 
and  take  a  charge  of  250  Ib.  apiece.  During  the  transfer  the  slag 
is  separated  from  the  metal  as  well  as  possible,  but  some  gets  into 
the  charcoal  fineries;  it  is  allowed  to  solidify  and  then  is  removed. 
Knobbling  Fire.  —  Upon  the  metal  is  now  charged  some  damp 
charcoal.  The  cold  blast  is  turned  on  and  the  metal  constantly 
agitated  and  raised  up  from  the  bottom  so  as  to  bring  it  in  contact 
with  the  blast.  Charcoal  is  added  from  time  to  time  and  is  kept 


70 


THE   METALLURGY  OF   IRON  AND   STEEL 


damp  to  avoid  loss,  and  the  slag  is  removed  at  intervals,  but  there 
must  always  be  a  layer  of  slag  between  the  metal  and  charcoal. 
As  the  metal  comes  to  nature,  it  is  pressed  together  with  the  pointed 
bar,  like  a  crowbar,  which  is  used  for  the  agitation  and  raising. 
At  the  end  of  about  an  hour  and  a  half,  the  ball  is  withdrawn  and 
hammered.  The  cinder  from  the  knobbling  fire  is  usually  charged 
into  the  melting  finery. 

The  great  advantages  of  the  knobbled  iron  as  compared  to 
puddled  iron  are  its  softness  and  relative  freedom  from  slag.  Tubes 
made  of  this  material  may  be  flanged  out  very  extensively  without 
showing  any  cracks,  and  rivets  will  flow  easily  when  hammered 
cold. 

The  Lancashire  Process.  —  In  the  Lancashire  process,  which 
some  believe  is  a  descendant  in  Sweden  of  the  purification  in  the 
two  fires  last  described,  the  same  operations  are  performed  in  one 
hearth,  which  is  made  of  iron  plates,  sometimes  cooled  with  water, 
with  a  tap-hole  in  the  front.  The  Swedish  Lancashire  process  is 


Swedish  Walloon 
Charcoal  Hearth 


FIG.  36.     From  Howe,  "The  Metallurgy  of  Steel." 

known  as  the  '  Walloon  process/  and  is  used  in  Sweden  for  making 
bar  iron  from  the  very  pure  pig  iron  reduced  from  Dannemora 
iron  ore.  This  bar  iron  is  used  in  Sheffield,  England,  for  conver- 
sion into  blister-steel,  and  some  of  the  steelmakers  pay  a  large 
price  for  it,  in  the  belief  that  it  has  a  certain  intangible  '  body '  not 


THE   PURIFICATION   OF   PIG   IRON 


71 


contained  in  wrought  iron  from  any  other  process,  and  which 
makes  a  superior  quality  of  steel.  It  is  probable,  however,  that 
this  body  is  wholly  imaginary.  The  process  consists  of  three 
stages : 

1.  The  melting  down,  which  is  somewhat  similar  to  the  opera- 
tion in  the  running-out  fire  or  melting  finery. 

2.  A    purification  period,  during  which  the  metal    is    nearly 
purified  and  comes  to  nature. 

3.  A  remelting  above  the  tuyere  for  further  purification. 

In  America,  pig  iron  heated  red-hot  in  the  chamber  H-C 
(Fig.  37),  during  the  working  of  a  previous  charge,  is  placed  be- 
tween two  layers  of  charcoal  and  a  little  above  the  level  of  the 


FIG. 


37. —  AMERICAN     LANCASHIRE     FURNACE.     Tu 
"The  Metallurgy  of  Steel." 


Tuyere.       From     Howe 


tuyere.  It  is  thus  quickly  melted,  the  liquid  drops  being  forced 
to  trickle  down  through  the  blast  and  thus  exposed  to  strongly 
oxidizing  conditions. 

The  second  period  begins  at  the  end  of  about  15  minutes,  when 
the  melted  metal  is  all  collected  in  the  bottom.  It  becomes  pasty 
in  contact  with  the  cold  hearth,  and  is  raised  by  a  pointed  bar  and 
charcoal  allowed  to  fall  under  it.  Some  slag  at  the  same  time  is 
tapped  off  and  some  is  mixed  with  the  pasty  lump,  which  pro- 
duces a  reaction  between  the  two  that  assists  in  the  purification. 
Toward  the  end  of  this  period,  which  lasts  20  or  25  minutes,  car- 
bonic oxide  comes  off  very  rapidly,  and  when  the  metal  becomes 
so  stiff  that  great  pressure  is  needed  to  raise  it,  and  the  slag  has 
become  thinner  and  whiter,  the  third  period  begins. 

The  metal  is  now  broken  into  pieces  and  raised  to  its  original 
position,  the  action  of  the  first  period  being  substantially  repeated. 
During  this  period  the  workman  is  careful  not  to  touch  the  mass 


72  THE  METALLURGY  OF  IRON  AND  STEEL 

collecting  in  the  bottom  of  the  hearth  lest  he  mix  slag  with  it.  By 
the  time  about  two-thirds  of  the  metal  is  melted,  some  rich  iron 
oxide  slag  is  added  in  order  to  keep  enough  in  the  bottom  of  the 
hearth  to  protect  the  metal  from  being  carburized  by  the  charcoal. 
When  all  the  metal  has  melted  and  dropped  down  in  front  of  the 
tuyere,  the  pasty  ball  is  pried  out  of  the  hearth  and  hammered. 
The  third  period  takes  about  25  to  30  minutes. 

Walloon  Process.  —  In  the  Swedish  Lancashire  or  Walloon  proc- 
ess, the  long  pigs  of  metal  are  fed  slowly  down  into  the  fire,  so  that 
it  is  not  nece  sary  to  constantly  pry  them  up  with  bars.  The 
charges  are  smaller  and  the  product  is  more  liable  to  be  hetero- 
geneous, because  the  first  melted  metal  is  decarburized  more  than 
the  last,  and  this  heterogeneousness  is  not  removed  by  the  re- 
melting.  (See  Fig.  36.) 

GENERAL  REFERENCE  BOOKS  ON  STEEL 

30.  Henry  M.  Howe.     "The  Metallurgy  of  Steel."     Vol.  i.  1890. 

New  York.  This  is  the  recognized  standard  authority  on 
the  metallurgy  of  the  Bessemer  and  crucible  steel  processes, 
and  upon  the  properties  of  steel  as  far  as  they  were  known 
and  understood  at  the  time  when  this  book  was  written. 
It  will  long  remain  a  classic.  There  have  been  many  edi- 
tions of  different  dates,  but  no  change  in  text  since  1890. 

31.  F.  W.Harbord.     "The  Metallurgy  of  Steel."    1905.     London. 

With  a  Section  on  Mechanical  Treatment  by  J.  W.  Hall. 
Next  to  No.  30,  this  is  the  most  complete  and  thorough 
book  on  steel  ever  written,  and,  for  English  readers,  will  be 
the  first  source  of  reference  for  those  desiring  recent  prac- 
tice. The  section  on  mechanical  treatment  is  the  best 
extant. 

32.  A.  Ledebur.     "Handbuch  der  Eisenhuettenkunde."     Fourth 

edition.  1902.  Leipzig.  This  is  an  excellent  reference 
book  for  those  who  read  German,  and  contains  a  very  com- 
plete account  of  the  metallurgy  of  both  iron  and  steel,  and 
of  their  properties.  There  are  also  classified  lists  of  the 
literature  upon  each  of  the  branches  of  the  subject. 

33.  Hermann  Wedding.     "  Ausfuehrliches  Handbuch  der  Eisen- 

huettenkunde."  Braunschweig.  1906.  Four  volumes. 
This  is  an  edited  translation  of  Percy's  "Iron  and  Steel/' 


THE   PURIFICATION   OF   PIG   IRON  73 

brought  up  to  date  and  greatly  enlarged  with  especial  ref- 
erence to  German  practice,  which  is  the  second  largest  in 
the  world. 

34.  H.  Noble.     "Fabrication  de  1'Acier."     Paris,     1905.     As  its 

name  indicates  this  book  deals  chiefly  with  the  manufacture 
of  steel,  the  section  on  properties  being  very  small. 

35.  Leon  Gages.     "Traite  de  Metallurgie  du  Fer."     In  two  vol- 

umes. Paris.  1898.  The  first  volume  covers  the  manu- 
facture of  iron  and  steel,  and  the  second,  foundry,  mechan- 
ical treatment  and  properties. 

36.  Sir  I.   Lowthian   Bell.     "Principles  of  the  Manufacture   of 

Iron  and  Steel. "  London.  1884.  This  book  well  accom- 
plishes its  aim,  namely,  to  elucidate  the  principles  of  iron 
and  steel  manufacture,  and  no  man  can  be  either  so  well 
informed  or  so  ignorant  as  not  to  understand  the  metal- 
lurgy of  these  metals  better  after  reading  it. 

37.  John  Percy.     "Metallurgy.     Iron  and  Steel."     London.  1864. 

This  classical  book  is  now  chiefly  valuable  for  historical 
reasons,  where  its  usefulness  is  often  unexpectedly  advan- 
tageous, as,  for  example,  in  patent  litigations,  but  at  the 
time  it  was  written  it  was  a  model  for  wealth  of  informa- 
tion (although  badly  arranged). 


IV 

THE  MANUFACTURE  OF  WROUGHT  IRON  AND 
CRUCIBLE  STEEL 

THE  MANUFACTURE  or  WROUGHT  IRON 

Pig  Iron  Used.  —  The  pig  iron  employed  is  of  the  grade  known 
as  'forge  iron7  or  'mill  iron/  In  the  United  States  we  prefer  to 
have  this  contain  about  1  per  cent,  of  silicon,  because  the  higher 
the  silicon  the  larger  will  be  the  amount  of  slag  made,  while  if  it  is 
too  low  the  iron  will  be  oxidized  excessively.  Manganese  is  usu- 
ally about  0.50  per  cent.,  although  it  varies  anywhere  from  0.25 
per  cent,  to  over  1  per  cent.,  depending  on  what  the  blast  furnace 
puts  in  the  pig.  Phosphorus  is  preferred  to  be  less  than  1  per  cent., 
and  sulphur  not  more  than  0.10  per  cent.,  because  neither  of 
these  elements  are  entirely  eliminated  during  the  process.  A 
large  amount  of  phosphorus  in  wrought  iron  is  not,  however,  as 
objectionable  as  it  is  in  steel,  because  the  slag  mechanically  mingled 
with  the  wrought  iron  hinders  it  from  being  brittle  under  shock, 
which  is  the  chief  damage  caused  by  phosphorus.  Pig  iron  con- 
taining 2.50  per  cent,  and  even  3  per  cent,  of  phosphorus,  and  as 
much  as  0.35  per  cent,  of  sulphur,  is  sometimes  used.  The  larger 
the  amount  of  impurities  the  larger  the  loss  of  metal  in  the 
process. 

Puddling  Furnaces.  —  There  are  many  different  varieties  of  pud- 
dling furnace,  varying  in  capacity  from  300  to  1500  Ib.  and  even 
more,  but  the  commonest  is  probably  the  500-lb.  furnace,  built 
either  single  or  in  pairs,  back  to  back,  the  latter  arrangement  hav- 
ing the  advantage  of  reducing  loss  of  heat  by  radiation,  which  is 
always  a  very  large  factor.  Puddling  furnaces  are  heated  by  gas 
or  bituminous  coal.  The  commonest  method  is  a  deep  bituminous- 
coal  fire,  giving  a  long  flame,  and  with  a  large  area  of  grate  in  rela- 
tion to  the  area  of  the  hearth,  in  order  that  a  high  temperature 
may  be  maintained. 

Fettling.  —  The  hearth  is  lined  or  'fettled7  with  oxide  of  iron  in 

74 


MANUFACTURE  OF  WROUGHT  IRON  AND  CRUCIBLE  STEEL      75 

the  form  of  roll  scale,  or  high-grade  iron  ore,  or  'bulldog/  i.e., 
roasted  puddle  cinder,  and  this  oxide,  together  with  the  metal 


FIG.  40.  —  500-LB.  PUDDLING  FURNACE. 


oxidized  during  the  melting,  supplies  the  base  which  automatically 
maintains  a  very  basic  slag  and  also  serves  as  the  principal  oxidiz- 


FIG.   41.  —  1500-LB.    PUDDLING   FURNACE. 
(Two  work  doors.) 

ing  agent  of  the  impurities.     The  fettling  is  repaired  between  melts 
as  often  as  is  necessary,  and  suffers  wear  with  each  operation. 


76 


THE  METALLURGY  OF  IRON  AND   STEEL 


Squeezers.  —  A  very  common  form  of  squeezer  is  that  shown  in 
Fig.  42,  the  distance  between  the  inner  and  outer  circle  being 


FIG.    42. —  ROTARY   SQUEEZER. 

greater  on  the  entering  side  than  on  the  outgoing  side.     As  the 
inner  circle  revolves,  the  corrugations  on  the  surface  carry  the  ball 


FIG.    43.  — ROE   MECHANICAL   PUDDLING   FURNACE. 

around,  giving  it  at  the  same  time  a  movement  of  rotation.     By 
the  time  the  ball  exits  on  the  opposite  side,  it  has  been  squeezed 


MANUFACTURE  OF  WROUGHT  IRON  AND  CRUCIBLE  STEEL      77 

and  kneaded  sufficiently  to  get  rid  of  a  large  amount  of  slag.  In 
European  countries  the  squeezer  is  rarely  used  and  the  ball  is 
'  shingled  '  -  —  reduced  under  a  hammer  —  to  weld  its  particles  to- 
gether. 

Mechanical  Furnaces.  —  The  labor  in  puddling  is  very  severe 
on  the  men,  and  many  attempts  have  been  made  to  remedy  this 
by  mechanical  furnaces  which  will  work  the  charge  without  so 
much  manual  labor.  Several  forms  of  mechanical  appliances  and 


FIG.  44. —  CHARGING  THE  PUDDLING  FURNACE. 

of  mecnanical  furnaces  have  been  invented,  but  without  any  per- 
manent success.  However,  the  mechanical  furnace  shown. in  Fig. 
43,  devised  by  James  P.  Roe,  of  Pottstown,  Pa.,  has  given  approxi- 
mately satisfactory  results.  It  is  suspended  on  trunnions,  and 
the  water-cooled  bottom  and  sides  are  lined  with  magnesite  brick. 
The  oil  and  blast  for  combustion  enter  through  the  two  trunnions 
and  the  products  of  combustion  escape  through  a  stack  at  each  end, 
which  meet  above  the  top  of  the  furnace  and  discharge  into  the 
atmosphere  as  shown.  The  furnace  is  made  to  oscillate  65°  each 
way  from  the  vertical,  which  keeps  the  slag  and  bath  uniformly 


78  THE  METALLURGY  OF   IRON   AND   STEEL 

mixed  and  avoids  the  hand-rabbling  of  the  ordinary  puddling  proc- 
ess. The  whole  charge,  weighing  about  4000  lb.,  is  discharged  in 
one  ball  by  sliding  it  down  the  hearth  of  the  furnace  toward  the 
end,  and  then  out  into  a  hydraulic  squeezer  of  special  design,  in 
which  it  is  compressed  in  three  dimensions  until  it  is  a  slab  and 
ready  for  rolling. 

Puddling.  —  The  pig  iron  is  usually  charged  by  hand  through 
the  working  doors  of  the  furnace,  and  the  puddler's  assistant  fires 
vigorously  in  order  to  melt  it  down  as  fast  as  possible,  which  usu- 
ally takes  about  30  to  35  minutes.  As  soon  as  melted,  there  fol- 
lows a  short  stage  of  7  to  10  minutes,  during  which  iron  oxide  in  the 
form  of  roll  scale  or  very  high-grade  iron  ore  is  added,  in  order  to 
make  a  very  basic  slag,  the  charge  being  thoroughly  mixed  and 


FIG.   45.  —  PUDDLING. 

cooled,  for  which  purpose  the  damper  is  put  on  and  sometimes 
even  water  is  thrown  on  to  the  bath.  The  object  is  to  reduce 
the  temperature  to  the  point  where  the  slag  will  commence  to 
oxidize  the  impurities  and  especially  the  phosphorus  and  sulphur 
ahead  of  the  carbon.  As  soon  as  the  reaction  is  started,  light 
flames  begin  to  break  through  the  covering  of  slag,  produced  by 
burning  carbon  monoxide  from  the  oxidation  of  carbon : 

1.  Fe2O3  +  3C=  SCO  +  2Fe; 

2.  CO  +  O  =  CO2. 

If  the  slag  is  not  very  basic  at  this  time  the  CO  will  reduce 
"phosphorus  and  sulphur  and  cause  them  to  return  to  the  metal. 


MANUFACTURE  OF  WROUGHT  IRON  AND  CRUCIBLE  STEEL      79 

As  the  carbon  monoxide  forms  more  and  more  abundantly,  the 
charge  is  more  violently  agitated  by  its  escape,  and  the  'boil'  is  in 
progress.  The  formation  of  gas  in  its  interior  causes  the  charge  to 
swell  greatly,  and  it  thus  rises  in  the  furnace  and  a  large  amount  of 
slag  pours  out  of  the  slag-hole  and  into  a  waiting  buggy.  About 
one-half  of  all  the  slag  produced  during  the  process,  and  amounting 
to  about  one-eighth  to  one-quarter  of  the  weight  of  the  metal 


FIG.   46. —  THE   BOIL. 

(A  removable  iron  shield  down  which  water  flows  protects  the  puddler  from  the  heat.) 

charged  to  the  furnace,  is  removed  at  this  time.  The  boil  con- 
tinues from  20  to  25  minutes,  and  during  this  time  the  puddler 
stirs  or  'rabbles'  the  charge  vigorously  with  a  long  iron  rabble, 
shaped  like  a  hoe.  Toward  the  end  of  the  boil  the  metal  begins  to 
come  to  nature,  and  points  of  solid  metal  project  through  the  cover 
of  slag,  while  other  pasty  masses  form  on  the  bottom  of  the  fur- 
nace. Both  of  these  things  must  be  corrected  immediately  by  the 


80  THE   METALLURGY   OF    IRON   AND   STEEL 


FIG.    47. —  GETTING   A   HOLD    OF   THE    BALL. 

puddler,  lest  (1)  the  iron  that  is  exposed  to  the  furnace  gases  be- 
come too  much  oxidized,  (2)  lest  the  iron  sticking  to  the  cold  bot- 
tom become  too  much  chilled,  or  (3)  lest  the  charge  be  not  uniform 


FIG.    48. —  TAKING   THE    BALL    OUT. 


MANUFACTURE  OF  WROUGHT  IRON  AND  CRUCIBLE  STEEL      81 

in  composition.  Finally,  the  whole  charge  comes  to  nature  and 
the  'balling'  period  begins  and  occupies  about  15  to  20  minutes. 
During  this  period  the  bath  is  divided  into  three  or  four  portions, 
which  are  each  rolled  up  into  a  ball,  consisting  of  a  large  number  of 
particles  partially  welded  together.  The  balls  are  rolled  up  near  the 
fire-bridge  in  order,  first,  to  protect  them  from  direct  contact  with 
the  flame,  and  second,  to  keep  them  as  hot  as  possible  until  the 
puddler  can  draw  them,  so  that  the  slag  may  be  fluid  and  thus 


FIG.  49.  — THE  BALL  ENTERING  THE  SQUEEZER. 

more  easily  squeezed  out  of  the  metal.  The  balls  are  then  squeezed 
in  turn,  and  the  furnace  hearth  repaired  for  another  charge.  The 
total  time  between  operations  is  usually  from  1  hour  and  10  min- 
utes to  1  hour  and  40  minutes. 

Chemistry  of  the  Process.  -  -  The  removal  of  the  impurities 
during  the  puddling  process  are  shown  in  Table  XI,  which  is 
quoted  because  it  records  probably  the  first  successful  attempt 
ever  made  to  study  in  this  way  the  chemistry  of  an  iron  or 


82 


THE  METALLURGY  OF   IRON  AND   STEEL 


TABLE  XL  — REMOVALS  IN  HAND  PUDDLING 
By  Calvert  and  Johnson,  Phil.  Mag.,  1857. 


Time 
after 
charging 

C 

Si 

s 

P 

Sample  No.  1 

Hrs.    Min. 
0           0 

Per  cent. 

2  275 

Per  cent. 
2   720 

Per  cent. 
0   301 

Per  cent. 
0   645 

..           ..    .> 

0       40 

2  726 

0   915 

«          "3   

1       00 

2  905 

0  197 

«          «    ^ 

1         5 

2  444 

0  194 

«          "5  

1       20 

2  305 

0  182 

«               a     Q 

1       35 

1  647 

0  183 

a             "7 

1       40 

1  206 

0  163 

«               a     g 

1       45 

0  963 

0  163 

«              «     g 

1       50 

0  772 

0  168 

Puddled  bar  

0  296 

0  120 

0   134 

0  139 

steel   process.     A   similar   study  is   graphically  represented    in 
Fig.  53. 

During  the  melting-down  stage,  the  silicon  and  manganese  in 
the  puddling  charge  are  almost  entirely  eliminated,  and  these  re- 
actions are  as  complete  as  they  will  be  by  the  end  of  the  '  clearing  ' 
stage  which  follows  it.  Much  phosphorus  and  sulphur  are  also 


FIG.   50.  — PUDDLE   ROLLS. 


removed.  The  boil  period  is,  of  course,  the  period  during  which 
the  carbon  escapes  together  with  all  the  phosphorus  and  sul- 
^phur  which  was  not  removed  during  the  first  two  periods. 


MANUFACTURE  OF  WROUGHT  IRON  AND  CRUCIBLE  STEEL     83 

Fuel.  —  The  temperature  of  the  puddling  process  is  as  high 
as  can  be  obtained  in  furnaces  of  this  type  without  preheat- 
ing the  air.1  The  result  is  a  very  large  waste  of  heat  up  the 


FIG.    51. —  ROLLING   PUDDLE    BAR. 


chimney,  although  some  economy  in  this  respect  is  obtained 
by  placing  boilers,  or  else  furnaces  to  heat  metal  for  the  rolls, 
where  they  will  receive  the  waste  heat  of  the  puddling  furnaces. 
The  two  greatest  items  of  expense 
in  the  puddling  process  are  the  fuel 
used  and  the  excessive  labor,  which, 
on  account  of  the  strength  and  en- 
durance demanded,  receives  a  high 
price.  The  amount  of  fuel  burned  per 
ton  of  iron  produced  will  usually  be 
about  one  ton  of  a  soft  bituminous 
coal,  or  a  little  more,  although  better 
figures  than  this  are  obtained  in  some 
cases. 

Losses.  —  The  loss  in  the  puddling 
process  usually  averages  from  4  to  6 
per  cent,  of  the  weight  of  the  metal 
charged,  although  so  much  iron  oxide 
is  added  or  is  reduced  from  the  lining  by  the  impurities  in  the 
metal,  that  in  the  Roe  furnace  the  wrought  iron  produced  will 

1  Indeed,  in  some  cases  the  air  is  preheated  by  the  regenerative  process, 
although  this  is  not  the  usual  practice. 


FIG.  52. —WROUGHT  IRON 
SHOWING  STRINGS  OF 
SLAG  MAGNIFIED  50 
DIAMETERS. 

(Unetched.) 


84 


THE  METALLURGY  OF   IRON  AND   STEEL 


actually  weigh  more  than  the  pig  iron  charged.     The  following 
table  gives  a  typical  example  of  loss : 

TABLE  OF  LOSSES  IN  HAND  PUDDLING 

Percentage  of 
Loss 

Silicon  burned 1 . 00 

Carbon  burned 3 . 50 

Sulphur  burned .20 

Phosphorus  burned 50 

Manganese  burned V.      .30 

Total 5.50 

Iron  reduced  from  oxide1  =1 .00  per  cent,  gain 
Net  loss 4.50 

1  There  is  much  iron  oxidized  and  carried  off  in  the  slag,  but  there  is  also 
much  reduced  by  impurities.  The  figure  here  given  represents  the  excess  of 
reduction  over  oxidation;  in  some  cases  it  runs  as  high  as  6  per  cent,  or  more. 


100 


10     20     30     40     50     60     70     80     90    100 

Time  (Minutes) 

FIG.  53.  — REMOVALS  IN  HAND  PUDDLING. 


MANUFACTURE  OF  WROUGHT  IRON  AND  CRUCIBLE  STEEL      85 

Slag.  —  The  slag  which  runs  from  the  tap-hole  during  the  boil 
is  known  as  'boilings/  while  that  tapped  out  at  the  end  of  the 
process  is  known  as  'tappings'  or  'tap-cinder/  The  characteris- 
tics of  the  boilings  are  that  they  contain  a  larger  amount  of  the  phos- 
phorus than  the  tappings,  and  also  that  globules  of  metallic  iron 
are  carried  off  in  the  violent  agitation  of  the  boil.  An  analysis  of 
the  two  varieties,  giving  a  mean  composition  from  seven  heats,  is  as 
follows : 1 


Boilings 

Tappings 

Ferric  oxide  (Fe-^Os).  . 

6  94 

12  90 

Ferrous  oxide  (FeO)    . 

62  61 

64  62 

Silica  (SiOa)  

19  45 

15  47 

Phosphoric  anhydride  (P2O5).   . 

6  32 

3  91 

Not  determined  (MnO,  S,  CaO,  etc.)..  

4.68 

3.10 

100.00 

100.00 

Total  iron.  . 

53  55 

59  29 

The  amount  of  slag  will  depend  chiefly  upon  the  amount  of 
silicon  in  the  pig  iron.  It  will  average  in  weight  about  one-half 
the  weight  of  the  charge,  where  the  silicon  is  high,  as  in  English 
practice  (say  1.70  to  2  per  cent.),  and  about  one-quarter  to  one- 
third  in  American  practice,  where  the  silicon  is  about  1  per  cent. 


THE  CARBURIZATION  OF  WROUGHT  IRON 

Wrought  iron  is  converted  into  steel  by  the  operation  of  car- 
burizing,  or  the  adding  of  carbon  to  it.  This  is  to-day  accom- 
plished in  two  ways:  (1)  By  the  cementation,  or  steel  conversion, 
process,  in  which  carbon  is  allowed  to  soak  into  red-hot  steel  in  a 
manner  like  in  nature  to  the  absorption  of  ink  by  blotting  paper; 
and  (2)  by  the  crucible  process,  in  which  wrought  iron  is  melted 
in  a  crucible  with  carbon,  or  with  iron  containing  carbon,  e.g., 
cast  iron. 

Cementation  Process.  —  We  have  already  observed  in  describ- 
ing the  blast-furnace  process  that  iron  at  a  bright-red  heat  will 
absorb  carbon  very  slowly.  The  action  appears  to  be  a  traveling  of 
solid  carbon  into  the  interior  of  solid  iron,  forming  with  it  a  chemi- 

1  Page  297  of  Number  40,  page  93. 


86 


THE  METALLURGY  OF   IRON  AND   STEEL 


cal  compound  or  carbide,  FeaC,  to  which  Professor  Howe  has  given 
the  name  of  'cementite.'  When  the  steel  is  at  a  proper  heat,  the 
rate  of  travel  is  approximately  f  of  an  inch  per  24  hours. 

Steel  Converting  Furnace.  —  A  section  of  the  type  of  cementa- 
tion-furnace used  in  Sheffield,  England,  is  shown  in  Fig.  55.  The 
superstructure,  e,  is  a  mere  chimney  for  the  purpose  of  carrying 

off  the  products  of  combustion 
from  the  fire  at  c,  and  for  re- 
ducing loss  of  heat  by  radiation. 
The  real  furnace  is  the  part  un- 
derneath this  superstructure  or 
stack,  and  it  has  several  small 
chimneys  of  its  own.  The  two 
converting  pots  are  shown  un- 
derneath the  points  a  a.  In 
Sheffield  they  are  built  of  stone 
and  are  2J  to  4  ft.  wide  and 
deep,  and  8  to  15  ft.  long.  On 
the  bottom  of  the  pot  is  first 
placed  a  layer  of  charcoal  in 
small  pieces  freed  from  dust. 
On  this  is  laid  a  layer  of  the 
wrought-iron  bars  to  be  con- 
verted, which  are  2  to  5  in. 
wide,  i  to  J  in.  thick,  and  nearly 
as  long  as  the  pot.  A  little 
space  is  left  (about  J  in.)  be- 
tween each  pair  of  bars  in  order 
that  they  may  be  completely 
surrounded  by  the  charcoal. 
On  top  of  the  layer  of  bars  is 

then  placed  another  layer  of  charcoal,  and  then  a  layer  of  bars, 
and  so  on  until  the  pots  are  filled,  each  one  containing  from  10 
to  30  tons  of  iron.  The  top  of  the  pots  is  then  luted  air-tight 
and  the  fire  lighted. 

In  about  2  days  the  temperature  has  reached  a  full  red-heat  of 
say  650°  to  700°  C.  (1200°  to  1300°  F.),  and  this  is  maintained 
from  7  to  11  days  longer,  depending  upon  the  grade  of  steel  to  be 
made.  The  names  of  the  different  grades  of  steel  made  in  Shef- 
field are  as  follows: 


•"•''/A*.  -  '.  ......  ~ /<:, 

FIG.    55.  —  CEMENTATION    FURNACE. 


MANUFACTURE  OF  WROUGHT  IRON  AND  CRUCIBLE  STEEL      87 

No.  1.     Spring  heat 0.50  per  cent,  carbon 

'    2.     Country  heat 0.60 

'    3.     Single-shear  heat 0.75 

'    4.     Double-shear  heat 1 . 00 

'    5.     Steel-through  heat 1 . 25 

1    6.     Melting  heat 1 .50 

The  product  is  controlled  by  a  series  of  trial  bars  which  are  so 
placed  that,  beginning  about  7  days  from  the  full-red  heat,  they 
can  be  withdrawn  from  the  furnace  from  time  to  time,  broken, 
and  examined.  The  appearance  of  the  fracture  denotes  the  ex- 
tent of  the  cementation. 

Discharging  the  Furnace.  —  When  the  cementation  has  pro- 
ceded  to  the  desired  point,  the  fire  is  withdrawn  and  the  furnace  is 
allowed  to  cool  for  about  a  week,  when  the  pots  are  opened  and 
the  bars  withdrawn  through  the  door  b. 

Blister-Steel.  —  The  product  of  the  cementation  process  is 
known  as  l  blister-steel'  because  its  surface  is  covered  with  blisters, 
due  to  the  formation  of  gas  by  a  reaction  between  the  carbon  of  the 
cementite  and  the  slag  contained  in  the  wrought  iron: 

C  +  FeO  =  CO  +  Fe. 

The  blister-steel  has  gained  about  1  per  cent,  in  weight  over 
the  wrought  iron  and  the  appearance  of  the  fracture  is  entirely 
different,  as  the  broken  surface  now  shows  large  bright  crystals. 

Shear-Steel.  —  The  bars  of  blister-steel  are  sometimes  forged  to 
a  smaller  size,  piled  up,  and  then  the  pile  forged  down  again  into  a 
bar,  which  makes  what  is  known  as* 'single  shear-steel/  Single 
shear-steel  may  be  again  piled  and  forged  into  double  shear-steel.  In 
America,  however,  it  is  more  common  to  melt  the  blister-steel  in 
crucibles,  which  separates  the  metal  from  the  slag  it  contains  and 
produces  the  finest  quality  of  cutlery  and  tool-steel  that  is  made 
in  America. 

Crucible  or  Cast  Steel.  —  The  cementation  process,  on  account 
of  the  length  of  time  and  the  very  large  amount  of  fuel  required, 
has  now  been  largely  superseded  by  the  crucible  process.  In  this 
process  the  wrought  iron  is  cut  up  into  small  pieces  and  melted  in 
covered  crucibles,  the  desired  amount  of  carbon  being  placed  on  top 
of  the  charge  before  the  melting,  together  with  any  other  alloying 
element  desired,  such  as  chromium,  tungsten,  manganese,  etc. 

Furnaces.  —  In  Sheffield,  England,  coke-furnaces,  or  melting- 
holes,  containing  each  two  crucibles,  are  almost  universally  used, 


88 


THE   METALLURGY  OF   IRON   AND   STEEL 


while  in  America  gas-furnaces,  containing  about  6  crucibles  each, 
are  the  common  type.  In  the  gas-furnace  it  is  necessary  that  the 
gas  and  air  for  combustion  shall  be  preheated,  in  order  that  we  may 
(1)  obtain  fuel  economy  and  (2)  reach  the  desired  temperature  for 
melting  quickly. 

Regenerative  Furnace.  —  The  operation  of  the  regenerative- 
furnace  is  shown  in  Fig.  57.  The  gas  enters  the  gas  regenerative- 
chamber  and  passes  up  between  the  checker-work  of  bricks,  laid 


FIG.    56. —  SECTION   THROUGH   SHEFFIELD 
MELTING   HOUSE. 


with  many  spaces  between,  and  into  the  melting-hole.  The  air 
enters  and  passes  up  through  its  regenerative-chamber,  meeting 
the  gas  above.  They  there  combine  and,  passing  through  the 
melting-hole,  divide  into  two  parts  and  pass  through  the  regenera- 
tive-chambers on  the  other  side.  Previous  to  beginning  the  opera- 
tion, all  of  the  brickwork  in  the  regenerative-chambers  has  been 
heated  red-hot  by  means  of  a  wood  fire.  The  gas  and  air  have 
therefore  absorbed  a  good  deal  of  heat  from  the  brickwork 
before  they  meet.  As  they  pass  down  through  the  regenerators 
on  the  outgoing  side,  they  will  still  further  increase  the  heat  of 
this  brickwork,  giving  up  their  temperature  to  the  checker- 


MANUFACTURE  OF  WROUGHT  IRON  AND  CRUCIBLE  STEEL      89 

work.  This  causes  them  to  go  to  the  stack  at  a  relatively  low  tem- 
perature, and  when  the  current  of  air  and  gas  is  reversed,  each 
now  entering  from  the  other  side,  they  become  more  highly  pre- 
heated than  before,  and  now  serve  to  heat  the  opposite  pair  of 


FIG.  57.  —  REGENERATIVE  GAS  CRUCIBLE  FURNACE  OR  "MELTING-HOLE." 

regenerators.  When  all  four  regenerators  have  been  raised  to  a 
high  temperature,  the  reversal  of  direction  takes  place  every  20 
minutes,  and  thus  a  uniformly  high  heat  is  obtained  with  low 
temperature  of  chimney  gases  and  consequent  fuel  economy. 


90  THE   METALLURGY   OF   IRON   AND   STEEL 

Crucibles.  —  In  England,  the  crucibles  are  made  of  fire-clay. 
They  are  usually  made  by  hand  at  the  steel  melting  plants  and 
are  dried  for  one  or  two  months,  on  a  shelf  next  to  the  chimney  of 
the  melting-furnace.  Before  being  used  they  are  heated  to  red- 
ness in  an  annealing  furnace  and  are  then  ready  to  receive  a  charge 
of  50  Ib.  of  metal.  The  clay  is  deeply  cut  by  the  slag,  and  there- 
fore the  charge  must  be  reduced  to  44  Ib.  for  the  second  melt  and 
38  Ib.  for  the  third,  in  order  that  the  slag-line  may  be  lower  each 
time.  After  the  third  melt  they  are  thrown  away.  The  advan- 
tages of  clay  crucibles  are  that  the  first  cost  is  lower,  and  that  they 
do  not  give  up  any  carbon  to  the  metal,  so  that  the  composition 
of  the  final  product  may  be  regulated  with  greater  exactness  and 
a  lower  carbon  steel  may  be  made,  if  desired. 

In  America,  the  crucibles  are  made  of  a  mixture  approximating 
50  per  cent,  graphite  and  50  per  cent,  fire-clay.  They  are  made 
and  tempered  by  factories  outside  of  the  steel-works  and  are  re- 
ceived by  the  latter  ready  for  use.  They  last  about  six  heats, 
after  which  the  bottom  is  sawed  off  and  used  for  the  top  of  a  new 
crucible.  They  hold  almost  100  Ib.  of  metal,  because  they  are 
stronger  than  clay  and  can  therefore  stand  greater  strains. 

Metal  Used.  —  Although  crucible  steel  is  supposed  to  be  made 
by  the  melting  of  pure  wrought  iron  with  charcoal,  washed  metal, 
ferromanganese  and  other  'physic/  it  is  not  at  all  uncommon  for 
the  wrought  iron  to  be  diluted  with  varying  amounts  of  cheaper 
scrap  steel,  which  unquestionably  lowers  the  quality  of  the  product. 
The  pieces  of  wrought  iron  are  put  into  the  crucible  first,  and  on  top 
of  that  is  placed  the  charcoal  or  pig  iron,  ferromanganese  or  spiegel- 
eisen,  and  various  physics,  such  as  salt,  potassium  ferrocyanide, 
oxide  of  manganese,  etc.  The  purpose  of  these  physics  is  not 
entirely  clear.  Probably  the  salt  and  oxide  of  manganese  make  a 
more  fluid  slag;  the  ferromanganese  puts  a  little  manganese  in  the 
steel;  and  the  ferrocyanide  may,  perhaps,  favor  the  absorption  of 
carbon  by  the  steel. 

In  some  cases  the  material  is  charged  directly  into  a  hot  cruci- 
ble from  the  previous  melt,  but  when  graphite  crucibles  are  used, 
these  are  sometimes  allowed  to  cool,  in  order  to  be  examined  for 
cracks,  because  the  breaking  of  a  crucible  in  the  furnace,  allowing 
the  liquid  mass  to  flow  out  upon  the  floor,  is  very  objectionable. 
There  is  a  hole  in  the  middle  of  the  floor  of  the  furnace,  so  that  if 
such  an  accident  happens  the  metal  may  run  down  into  a  pit 


MANUFACTURE  OF  WROUGHT  IRON  AND  CRUCIBLE  STEEL      91 

underneath ;  and  the  floor  is  also  covered  with  a  few  inches  of  coke- 
dust  to  absorb  the  metal  in  such  a  contingency. 

Melting.  —  The  crucibles  are  placed  in  the  furnace  and  the  gas 
and  air  turned  on,  in  the  case  of  a  gas-furnace.  In  the  case  of  a 
coke-furnace,  the  crucibles  are  placed  upon  their  fire-clay  stands 
and  the  coke  packed  around  them  upon  the  fire  left  from  the  last 
melt.  At  the  end  of  about  an  hour,  the  coke  fire  has  burned  down 


FIG.    58. —  STAGES    IN   CRUCIBLE   STEEL   MELTING. 

so  low  that  it  has  to  be  poked  down  and  more  coke  added.  The 
melting  takes  on  the  average  from  two  to  three  hours  in  both 
cases,  and  the  charge  is  examined  by  removing  the  crucible  cover, 
to  make  sure  that  it  is  entirely  molten.  The  coke  fire  also  requires 
further  attention  at  this  time,  and  care  must  be  taken  that  no  coke 
falls  into  the  crucible  when  the  cover  is  off. 

Killing.  —  When  the  charge  is  entirely  molten,  it  is  kept  in 
the  furnace  for  one-half  to  an  hour  longer  in  order  that  it  may  teem 
'dead/  that  is,  pour  quietly  without  the  evolution  of  gas,  and 
yield  solid  ingots.  If  the  'killing'  time  is  too  long,  the  ingots  will 
be  solid,  but  the  steel  will  be  hard,  brittle  and  weak,  probably  as 
a  result  of  the  absorption  of  too  much  silicon  from  the  walls  of  the 
crucibles.  Graphite  crucibles  probably  yield  more  silicon  than 
clay  crucibles.  Just  what  takes  place  during  the  killing  of  steel 
is  not  definitely  known.  Some  have  suggested  that  the  gas  con- 
tained in  the  steel  is  eliminated  from  it  during  this  time,  but  the 
alternate  suggestion  that  the  principal  effect  of  the  killing  is  to 
cause  the  steel  to  absorb  silicon,  becoming  sound  on  this  account, 
is  the  more  generally  accepted  one.  The  amount  of  silicon  in  the 
final  steel  will  vary  greatly,  but  will  average  perhaps  from  0.10  to 
0.50  per  cent. 

Pulling.  —  When,  in  the  judgment  of  the  melter,  the  steel  has 
been  properly  killed,  the  crucibles  are  removed  from  the  fire  by 
the  puller-out,  who  straddles  the  top  of  the  furnace  and  grasps  the 


92 


THE   METALLURGY   OF   IRON   AND   STEEL 


FIG.    59. —POURING. 


crucible  with  a  pair  of  tongs,  his  legs  and  arms  being  swathed  in 
wet  cloths  to  protect  him  from  the  heat,  and  his  eyes  frequently 
being  protected  by  heavy  blue  glasses.  The  puller-out  then  passes 
the  crucible  to  the  pourer,  who  pours  it  as  shown  in  Fig.  59,  the  slag 

first  being  swabbed  off  with  a 
ball  of  cold  slag  on  the  end  of 
an  iron  rod.  The  total  time  of 
operations  is  3J  to  5^  hours  in 
England,  and 
3J  to  4  hours 
in  America. 

Ingot  Molds. 
—  Ingot  molds 
are  shown  in 
Fig.  60,  and  as 
a  usual  thing 
each  mold  has 
a  capacity  to 
take  the  charge 

from  one  crucible.  The  metal  must  be  teemed 
into  this  with  great  care,  so  that  the  stream  shall 
not  touch  the  sides  during  pouring.  In  case  a 
large  ingot  is  to  be  poured,  then  several  cruci- 
bles are  poured  at  once  into  the  same  mold,  care 
being  taken  that  the  metal  shall  be  liquid  as  long 
as  the  pouring  continues. 

Grading.  —  The  composition  of  the  final  metal 
is  a  matter  of  some  uncertainty,  especially  as  re- 
gards the  carbon  and  silicon.  The  former  is  more 
easily  adjusted  when  clay  crucibles  are  used,  be- 
cause .the  amount  of  carbon  dissolved  from  a 
graphite  crucible  will  depend  to  a  large  extent 
upon  the  time  and  temperature  of  the  operation,  FIG.  eoT^  INGOT 
etc.  The  ingots  are  therefore  always  graded  after  ^RUCI  BLE 
they  have  cooled,  by  breaking  off  the  upper  part  STEEL.  From 
of  them,  which  contains  the  pipe  and  is  therefore  MetYiiurg^of 
useless,  except  when  remelted,  and  examining  the  steel." 
fracture  with  the  eye.  The  skilled  steel  man  can  thus  estimate  the 
carbon  within  0.10  per  cent.,  and  the  ingots  are  put  away  in  the  pile 
with  others  of  like  analysis.  At  large  American  works,  how- 


MANUFACTURE  OF  WROUGHT  IRON  AND  CRUCIBLE  STEEL      93 

ever,  this  grading   by  eye  is  always  supplemented  by  chemical 
analysis. 

Chemistry.  —  The  chemistry  of  the  crucible  process  is  very  sim-  ' 
pie,  and  consists  principally  in  the  elimination  of  the  slag  in  the 
wrought  iron  and  the  absorption  by  the  metal  of  carbon,  silicon 
and  manganese.  There  is  also  a  very  slight  increase  in  sulphur, 
which  perhaps  comes  from  the  pyrite  in  the  clay  or  graphite,  or 
from  sulphurous  gases  which  find  their  way  under  the  cover  of  the 
crucible.  Phosphorus  also  increases  slightly,  perhaps  from  the 
slag  out  of  the  wrought  iron. 

Loss.  —  The  loss  is  due  to  the  elimination  of  the  slag  and  to 
some  slight  oxidation  of  metal  by  oxygen  in  the  gas  inside  the 
crucible.  It  is  counteracted  to  some  extent  by  the  absorption  of 
carbon,  silicon  and  manganese,  and  will  average  slightly  more 
than  2  per  cent,  in  clay  crucibles  and  somewhat  less  than  2  per  cent, 
in  graphite  crucibles,  doubtless  due  to  there  being  less  oxidation 
in  the  presence  of  the  graphite. 

Fuel.  —  In  coke  fires,  the  amount  of  fuel  used  will  be  three  to 
four  times  the  weight  of  steel  produced.  In  gas-fired  furnaces  the 
amount  of  fuel  used  to  make  producer  gas  will  be  equal  to  or 
slightly  less  in  weight  than  the  amount  of  steel  produced.  The 
high  cost  in  making  crucible  steel  is  on  account  of  the  cost  of  cru- 
cibles, fuel,  labor  and  raw  material. 


REFERENCES  ON  THE  MANUFACTURE  OF  IRON 

There  is  but  one  American  book  (No.  47)  devoted  either  to  the 
manufacture  of  pig  iron  or  wrought  iron.  One  should  refer  to 
Nos.  2,  32,  33,  35,  36,  37,  and  the  list  given  below: 

40.  Thomas  Turner.     "  The  Metallurgy  of  Iron."  *     London,  1895. 

41.  A.  de  Vathaire.     "Les  Hautes  Fourneaux."     Paris. 

42.  H.  Bauerman.     "A  Treatise  on  the  Metallurgy  of  Iron."* 

London,  1868. 

43.  M.  A.  Pavlov.     "Atlas  of  Plans  for  Blast  Furnace  Construc- 

tion." Gekatermoslov  (Russia),  1902.  Although  these 
drawings  are.  lettered  in  Russian,  one  gets  much  valuable 
information  from  them  even  without  being  able  to  read  the 
language. 

*  Starred  books  refer  both  to  pig  iron  and  wrought  iron. 


94  THE  METALLURGY  OF  IRON  AND  STEEL 

44.  Frederick  Overman.    "The  Manufacture  of  Iron. "  *    Philadel- 

phia, 1850. 

45.  W.   Truran.     "The   Iron  Manufacture   of   Great   Britain/'* 

London,    1865.     Revised   by   J.   Arthur   Phillips   and  W. 
H.  Dorman. 

46.  James  P.  Roe.     "The   Development   of   the   Roe   Puddling 

Process/'    Journal,  Iron  and  Steel  Institute,  No.  Ill,  1906, 
pages  265-306. 

47.  Robert   Forsythe.     "The   Blast   Furnace  and  the  Manufac- 

ture of  Pig  Iron." 

*  Starred  books  refer  both  to  pig  iron  and  wrought  iron. 


THE  BESSEMER  PROCESS 

Pig  Iron  Used.  —  In  the  large  American  works,  pig  iron  for 
the  Bessemer  process  is  preferred  to  have  about  Lper  cent,  of 
silicon.  This  is  the  chief  slag  producer  and  also  the  chief  heat 
producer.  To  keep  it  at  a  low  figure  limits  the  amount  of  slag 
made,  which  limits  one  of  the  sources  of  iron  loss.  Furthermore, 
the  lower  the  silicon  the  shorter  will  be  the  time  of  blow;  but  it  is 
usually  risky  to  allow  it  to  fall  below  1  per  cent.,  or  the  blow  will 
be  cold,  and  it  is  only  by  very  rapid  working  and  permitting  the 
least  possible  delay  between  operations,  so  that  the  converter  and 
ladles  are  kept  very  hot,  that  we  are  able  to  get  along  with  as  little 
as  this.  The  manganese  is  below  0.8  per  cent.  This  also  fur- 
nishes heat;1  but  it  is  now  an  expensive  ingredient  of  pig  iron,  and 
also  has  the  effect  of  making  very  liquid  slags,  which  cause  a  good 
deal  of  slopping  or  'spitting'  from  the  converter  (i.e.,  ejection  of 
the  material  by  the  blast),  and  also  make  the  steel  ingots  dirty 
and  spotted  with  oxide  spots,  due  to  slag  carried  over  with  the 
steel.  Manganese  of  1.50  per  cent.,  with  silicon  of  1.00  to  0.90  per 
cent.,  gives  a  very  '  wet'  slag,  which  follows  the  metal  into  the  ladle 
and  boils  up  through  it,  oxidizing  the  manganese  in  the  steel : 

(1)  FeO+Mn  =MnO+Fe. 

The  phosphorus  and  sulphur  must  be  below  0.10  and  0.08  per 
cent.,  respectively,  in  order  that  the  steel  may  be  salable,  as 
neither  of  these  elements  is  reduced  in  the  acid  Bessemer  process. 

Mixer.  —  It  takes  about  two  blast  furnaces  to  supply  one  con- 
verter with  metal,  so  that  a  modern  plant  of  two  to  four  converters 
will  be  operated  in  conjunction  with  a  large  blast-furnace  plant. 
The  product  of  each  of  these  furnaces,  if  not  too  different  from  the 

1  Indeed,  formerly,  in  the  Swedish  Bessemer  practice,  the  pig  iron  con- 
tained 2  per  cent,  of  manganese,  and  this  element  was  relied  upon  as  the  chief 
source  of  heat,  because  silicon  was  necessarily  low  in  the  Swedish  charcoal 
pig  iron. 

95 


FIG.    65. —  A   BESSEMER   BLOW. 


THE   BESSEMER  PROCESS 


97 


desired  analysis,  will  be  poured  into  a  huge  reservoir,  or  'mixer/ 
capable  of  holding  150  to  500  tons,  which  is  then  used  as  a  source 
of  supply  for  the  converters. 

The  mixer  serves  several  very  useful  purposes:  (1)  It  equalizes 
the  irregularities  of  pig  iron  composition  by  mixing  the  product  of 
several  furnaces,  and  also  brings  the  composition  somewhat  under 
the  control  of  the  metallurgist  of  the  Bessemer  plant,  because  he 
not  only  can  pick  and  choose  from  the  different  furnac'es,  but  he 


FIG.    66.  — MIXER. 

has  a  few  large  cupolas  under  his  dominion  in  which  he  can  melt 
iron  of  any  desired  analysis  to  pour  into  the  mixer  and  help  regu- 
late its  contents. 

(2)  Because  of  its  large  size,  and  the  fact  that  it  is  continually  in 
receipt  of  new  fresh  metal,  the  mixer  can  keep  its  contents  molten 
for  an  indefinite  length  of  time,  whereas  a  ladle  containing  15  tons 
of  pig  iron  would  chill  up  in  a  very  few  hours.     Mixers  are  supplied 
with  blowpipes  which  can  contribute  a  small  amount  of  heat  to  the 
charge,  but  it  is  not  often  necessary  to  use  them. 

(3)  The  capacity  of  the  mixer  is  so  large  that  a  delay  either  at 
the  blast  furnace  or  at  the  steel-works  will  not  discommode  it 
greatly,  and  thus  each  operation  is  independent  of  the  other. 


98 


THE  METALLURGY  OF   IRON  AND   STEEL 


(4)  Pig  iron  in  the  mixer  suffers  a  slight  loss  in  sulphur,  be- 
cause manganese  sulphide  forms  and,  not  being  very  soluble  in 
iron,  slowly  passes  out  of  it  into  the  slag. 

Construction  of  the  Converter.  —  The  construction  and  dimen- 
sions of  the  converter  are  shown  in  Figs.  67  and  68.  It  consists  of 


FIG.  67.  —  FIFTEEN-TON  CONVERTER  SHELL.     From  Howe,  "The  Metallurgy  of 

Steel." 

a  steel  shell,  riveted  together  and  supported  by  two  trunnions  upon 
which  it  can  be  made  to  rotate.  One  of  these  trunnions  is  hollow, 
and  serves  as  a  wind-pipe  to  connect  the  blast  from  the  blow- 
engine  with  the  wind-box  at  the  bottom  of  the  vessel.  On  the 
other  trunnion  is  fastened  a  pinion,  which  engages  with  a  rack 
joined  to  a  hydraulic  piston  and  of  such  a  length  that  its  move- 
ment can  rotate  the  converter  through  an  angle  of  at  least  270°. 
The  lining  of  the  bottom  is  pierced  with  about  250  half-inch  holes, 
which  connect  the  wind-box  with  the  inside  of  the  converter  and 


THE   BESSEMER   PROCESS 


99 


serve  for  the  passage  of  the  blast.  The  shape  of  the  converter  is 
such  that,  when  it  is  lying  on  its  side,  the  metal  will  not  cover  any 
of  these  tuyere-holes.  This  is  necessary,  or  the  blast  could  never 
be  turned  off  without  having  molten  metal  run  down  into  the  wind- 
box.  The  converter  may  have  either  an  eccentric  or  a  concentric 
shape.  The  advantage  of  the  eccentric  shape  is  that  less  heat  can 
escape  from  the  nose :  the  advantage  of  the  concentric  shape  is  that 
the  vessel  may  contain  its  charge  when  turned  on  either  of  the 
sides. 

Lining.  —  The  lining  is  made  of  highly  refractory  acid  ma- 
terial composed  principally  of  silica.     In  England,  a  ganister  rock 


FIG.  68.  —  FIFTEEN-TON  CONVERTER  SECTION.      From  Howe,  "The  Metallurgy 

of  Steel." 

is  used,  or  sometimes  the  lining  is  rammed  up  around  a  pattern 
and  is  composed  of  silicious  material  held  together  by  a  small 
amount  of  fire-clay.  In  America,  it  consists  usually  of  blocks  of 
ganister  or  of  mica-schist  (a  silicious  rock  consisting  of  pseudo- 


100 


THE  METALLURGY  OF   IRON  AND  STEEL 


strata,  or  laminae,  formed  by  tiny  plates  of  mica)  laid  with  a  thin 
layer  of  refractory  fire-clay  between,  and  in  such  a  manner  that  the 
edges  of  the  laminae  will  be  exposed  to  the  wear  to  which  it  is 
subjected.1  After  a  new  lining  is  put  in,  it  is  carefully  dried,  and 
every  Sunday  afternoon,  before  the  converter  begins  its  operation 
for  the  week,  a  wood  fire  is  kept  in  it  for  several  hours  in  order  to 


FIG.  69."      From  Howe,  "The  Metal- 
lurgy of  Steel." 


FIG.    70.  —  ECCENTRIC    CONVERTER. 
From  Howe,  "The  Metallurgy  of  Steel." 


heat  the  lining  to  a  red  heat.  Between  the  heats  the  lining  is  re- 
paired, if  necessary,  with  balls  of  silicious  material  and  clay.  On 
Sundays,  and  with  an  occasional  lay-off  for  which  one  extra  shell 
is  provided,  more  extensive  repairs  are  made,  and  in  this  way  the 
lining  is  made  to  last  several  months,  —  say  10,000  to  20,000  heats. 
The  converter  slags  are  always  high  in  silica  and  corrode  the  lin- 
ing only  slightly.  If,  however,  any  uncombined  oxide  of  iron 
comes  in  contact  with  it,  it  is  attacked  very  rapidly.  For  this  rea- 
son the  mouths  of  the  tuyeres  are  rapidly  eaten  away,  and  this 
part  of  the  converter  lasts  only  about  20  to  25  blows.  The  bottom 

» If  we  represent  the  blocks  of  mica-schist  by  big  books,  and  lay  these 
books  in  a  horizontal  position  with  the  edges  of  the  leaves  exposed,  it  will 
illustrate  the  method  employed. 


THE   BESSEMER  PROCESS 


ioi 


is  therefore  fastened  to  the  body  with  links  and  keys,  so  that  it 
may  be  readily  detached  and  replaced  by  a  new  one.  Indeed,  in 
some  works  bottoms  are  changed  with  an  average  delay  to  the 
operation  of  only  about  20  minutes  for  each  replacement. 

Bottoms.  —  The  lining  of  the  bottom  is  made  by  placing  the 
tuyere-bricks  (see  Fig.  68)  in  position  and  then  filling  in  around 
them  with  refractory  material  consisting  of  damp  silicious  ma- 
terial held  together  with  clay  and  containing  usually  some  coke 
breeze,  which  seems  to  lessen  the  chemical  activity  of  the  corrosion. 
The  details  of  lining  vary  so  greatly  that  no  general  rules  can  be 
given.  The  number  of  tuyeres  is  from  18  to  30,  the  number  of 
holes  in  each  from  12  to  18,  and  the  size  of  the  holes  f  in.  (Eng- 
land) or  |  to  f  in.  (America).1  The  correct  lining  is  of  the  greatest 


FIG.  71.  —  CORROSION  OF  THE  BOTTOM  LINING  OF  BESSEMER  CONVERTER. 

importance  and  is  the  most  influential  factor  in  determining  the 
life  of  the  bottom,  which  furthermore  depends  upon  the  care  in 
drying,  the  temperature  of  blowing,  the  pressure  of  blast,  and  the 
composition  of  pig  iron.  A  bottom  should  dry  36  hours  or  more. 
Its  life  is  shortened  by  (1)  hotter  blows,  (2)  longer  blows,  (3)  lower 
blast  pressure  (because  the  blast  holds  the  metal  away  from  the 

1  The  acid  Bessemer  process  finds  its  greatest  importance  in  America,  and 
next  to  that  in  England.    Germany  is  the  leader  in  basic  Bessemer  practice. 


THE  METALLURGY  OF  IRON  AND  STEEL 

mouths  of  the  tuyeres),  and  (4)  more  manganese  in  the  pig  iron  (be- 
cause a  wet  slag  is  more  corrosive) .  Between  heats,  when  the  vessel 
is  on  its  side  receiving  the  recarburizer,  pouring  into  a  ladle,  or  re- 
ceiving a  new  charge,  the  lining  of  the  bottom  can  be  repaired. 
For  instance,  if  one  tuyere  eats  away  faster  than  its  fellows,  the  ex- 
cessive corrosion  can  be  prevented  by  stopping  it  up  with  mud, 
because,  if  no  air  passes  through  the  holes,  no  oxide  of  iron  is 
formed  at  their  mouths.  Or  a  worn  tuyere  may  be  replaced  by  a 
new  one,  etc.,  etc.  These  repairs  are  chiefly  made  through  the 
wind-box,  the  back  plate  of  which  is  removable. 

When  a  bottom  is  worn  out,  it  is  taken  away  and  a  new  one 
brought  on  a  car  and  placed  under  the  converter,  which  is  in  the 

vertical  position.  Around  the 
top  is  piled  a  ring  of  thick  wet 
mud,  and,  as  the  bottom  is  forced 
up  against  the  body  by  hydraulic 
pressure,  the  mud  is  squeezed 

shoulder ^^  /  No^e\      into  a  firm  joint.     Lack  of  space 

prevents  an  account  of  some  of 
the  interesting  expedients  that 
are  resorted  to  to  stop  an  oc- 
FIG.  72.  —  CONVERTER  PARTS.  casional  leak  in  this  joint  with- 
out delaying  the  first  heat,  which 

must  be  avoided  if  possible,  as  the  first  heat  on  a  new  bottom  is 
already  too  liable  to  be  a  cold  one. 

Operation  of  the  Converter.  —  Figs.  73  and  74  are  sections 
through  the  converter  plant  at  different  points.  In  Fig.  73,  A  is 
the  mixer,  capable  of  containing,  say,  300  tons  of  metal;  B  is  the 
ladle  carriage  from  the  blast  furnace,  from  which  the  ladle  C  has 
been  raised  to  pour  the  metal  into  the  mixer.  Immediately  above 
D  is  the  ladle  that  is  to  take  the  metal  from  the  mixer  to  the  con- 
verter, for  which  it  is  transferred  along  a  level  track  unti^  it  comes 
to  E  (Fig.  74),  where  it  is  poured  into  the  vessel,  now  in  the  hori- 
zontal position,  as  shown  by  the  dotted  line.  When  the  metal 
has  been  poured  in,  the  wind  is  turned  on  and  the  vessel  elevated 
into  the  vertical  position.  The  blast  now  pours  through  the  18 
inches  or  so  of  metal  in  the  bottom  of  the  converter  in  a  wide 
spray  of  tiny  bubbles  until  the  impurities  are  oxidized,  when  it 
is  turned  again  into  the  horizontal  position  and  trie  wind  cut  off. 
In  anticipation  of  this  a  predetermined  quantity  of  spiegeleisen 


THE  BESSEMER   PROCESS 


103 


has  been  tapped  from  the  spiegel  cupola  into  the  ladle  at  H  (Fig. 
73).     (For  soft  steel  ferromanganese,  not  spiegeleisen,  is  used.) 
Spiegeleisen  is  pig  iron  very  high  in  manganese.     Some  analyses 


are  given  in  Table  XII.  It  is  melted  in  the  spiegel  cupola  together 
with  a  predetermined  amount  of  high  silicon  pig  iron,  and  is  then 
used  to  recarburize  the  bath  in  the  vessel,  for  which  purpose  the 


Tom . 

FIG.   74. 


ladle  is  now  run  into  the  position  E  (Fig.  74)  and  its  contents 
poured  into  the  bath.     The  reactions  that  take  place  between  the 


104  THE   METALLURGY   OF    IRON   AND   STEEL 

TABLE    XII.  — ANALYSIS    OF    VARIOUS    GRADES    OF   PIG   IRON 


NAME 

Silicon 
Per  cent. 

Sulphur 
Per  cent. 

Phosphorus 
Per  cent. 

Manganese 
Per  cent. 

Carbon 
Per  cent. 

fNo.  1  

2.75 
2.25 
1.75 
1.25 
0  .  75  to  1  .  75 
0.80  to  2.  00 
under  1.00 

under  1  .  66 
0.50  to  1.00 
under  1  .  00 
under  1  .  00 
8.00  to  15.00 
50.00 
8.00  to  15.00 

0.035 
0.045 
0.055 
0.065 
0.05  to  0.30 
0.03  to  0.08 
under  0.10 
under  0.050 

under  0.03 
under  0  .  03 
under  0  .  05 
under  0.07 
under  0.02 
under  0.  01 

0.30  to  1.50 

0.30  to  3.  00 
under  0.10 
2.00  to  3.  00 
under  0  .  05 
0.10  to  2.00 
0.10  to  1.00 
0.10  to  0.50 
under  0.15 
0.10  to  0.50 
under  0  .  08 
under  0.15 

0.20  to  1.60 

0.20  to  1.50 
0.30  to  0.50 
1  .  00  to  2  .  00 
0  .  30  to  0  .  50 
1.00  to  2.  00 
80.00 
40.00 
15.00  to  30.  00 

3.00  to  4.00 

3.50  to  4.  00 

5.00  to  7.  00 
5.00  to  6.  00 
5.00  to  6.  00 
1.00  to  2.  00 
under  0.40 
1.00  to  1.50 

Foundry  j  No.  2  
Irons  ]  No.  3  

1  No.  4  
Forge 

Bessemer  —  Acid  
Bessemer  —  Basic  .... 
Open-hearth  —  Acid.  . 
Open-hearth  —  Basic.  . 
Ferromanganese  
Ferromanganese  
Spiegeleisen 

Ferrosilicon  

Ferrosilicon  

Silico-Spiegel  

15.00  to  20.  00 

elements  in  the  recarburizer  and  the  impurities  in  the  bath  are  as 
follows : 

(a)  Mn  +  FeO  =  MnO  +  Fe; 

(6)      C  +  FeO  =     CO  +  Fe. 

Reaction  (b)  produces  a  boil  of  the  bath,  which  serves  to  stir  it  well 
and  distribute  the  elements  uniformly.     Reaction  (a)  removes  a 


Converter. 


Cupola. 
Ladle. 
Runner. 


FIG.   75. —  POURING   METAL   INTO   THE   CONVERTER. 

large  amount  of  oxygen  from  the  metal  and  takes  some  of  the 
manganese  in  the  recarburizer  into  the  vessel  slag.     There  is  also 


THE   BESSEMER  PROCESS  105 

a  slight  loss  of  silicon  from  the  recarburizer  by  the  following  re- 
action : 

(c)  Si  +  2  FeO  =  SiO2  +  2  Fe. 

All  of  these  losses  are  discounted  in  calculating  the  composi- 
tion and  amount  of  metal  tapped  from  the  spiegel  cupola,  so  that 
there  should  be  left  in  the  steel  the  desired  percentage  of  carbon, 
silicon,  and  manganese. 

After  the  'spiegel  reaction'  is  completed,  the  steel  is  poured 
from  the  converter  into  a  ladle  held  at  the  point  0  by  the  jib-crane 
/,  or  by  one  of  the  traveling  cranes  K  or  L.  The  ladle  is  then  car- 
ried over  to  a  position  above  the  ingot  molds  into  which  the  steel  is 
to  be  teemed.  In  pouring  the  steel  into  the  ladle,  the  slag  is  held 
back  in  the  vessel  as  much  as  possible,  because  this  not  only  fur- 
nishes heat  for  the  next  operation,  but  also  makes  it  shorter  by  as 
much  as  20  or  25  per  cent.,  because  the  slag,  being  an  oxidized 
substance,  assists  in  oxidizing  the  impurities  in  the  next  charge. 

The  turning  on  and  off  of  the  blast  and  the  rotation  of  the  con- 
verter is  all  executed  by  the  blower,  who  stands  upon  the  pulpit  at 
W  and  operates  the  various  valves,  and  also  judges  by  eye  the 
progress  of  the  purification  from  the  appearance  of  the  flame  which 
issues  from  the  mouth  of  the  converter. 

Every  effort  is  made  by  him  to  so  arrange  the  different  opera- 
tions of  the  converter,  cranes,  and  ladles  and  to  bring  in  both 
spiegeleisen  and  iron,  that  each  step  shall  fit  into  the  others  without 
delay  to  the  operation  in  any  of  the  converters.  He  also  has  under 
his  control  means  for  lowering  the  temperature  of  the  bath,  if 
necessary :  (a)  By  ordering  an  amount  of  cold  steel  scrap  to  be 
thrown  into  the  mouth  of  the  vessel  during  the  blow1  and  (6)  by 
admitting  live  steam  into  the  converter  with  the  blast.  The  de- 
composition of  the  steam  very  quickly  reduces  the  heat  of  the 
blow.  Attempts  have  been  made  to  dispense  with  the  blower, 
who,  on  account  of  the  long  training  and  experience  necessary,  is 
the  most  highly  paid  man  in  the  plant,  next  to  the  foreman,  by 
judging  of  the  progress  of  the  operation  with  the  spectroscope; 
but  when  two  or  three  vessels  are  blowing  at  the  same  time  the 
reflected  light  from  one  interferes  with  the  spectroscopic  indica- 
tions of  the  others.  Furthermore,  the  spectroscope  gives  no  indi- 
cations of  the  temperature  of  the  blow,  and  until  the  past  two  or 

1  Scrap  is  so  valuable  for  use  in  the  open-hearth  process  that  (6)  is  now 
used  much  more  than  (a). 


106 


THE  METALLURGY  OF   IRON  AND   STEEL 


three  years  no  reliable  pyrometer  existed  which  was  suitable  for 
this  use. 

Steel  Ladles.  —  The  ladles  to  receive  the  steel  and  teem  it  into 
molds  are  steel  shells  lined  with  a  cheaper  grade  of  acid  refractory 
material,  because  the  life  of  these  ladles  is  limited  to  about  six 


FIG.    76.  —  FIFTEEN-TON   STEEL   TEEMING   LADLE. 


heats  by  the  wearing  out  of  the  nozzle,  and  therefore  a  more  ex- 
pensive lining  would  be  wasted.  The  arrangements  of  nozzles, 
stoppers,  and  handle  shown  in  Fig.  76  are  provided  in  order  that  a 
thin  stream  of  steel  may  be  poured  into  the  molds  and  may  be  in- 
terrupted when  a  new  mold  is  being  brought  into  place.  The  slag 
lies  on  top  of  the  metal,  and  when  this  begins  to  come  out  of  the 
nozzle  the  stopper  is  let  down  and  the  ladle  carried  over  a  slag  car 
and  turned  upside  down  to  dump  out  the  slag.  At  this  time  the 
blower  observes  the  lining  of  the  ladle  in  order  to  tell  whether  the 


THE   BESSEMER   PROCESS 


107 


steel  was  too  hot  or  too  cold.  If  there  is  a  skull  of  metal  frozen 
inside  the  ladle,  the  steel  was  too  cold;  if  there  is  no  frozen  metal, 
it  was  too  hot ;  but  if  there  is  a  spot  of  metal  here  and  there  on  the 
bottom,  it  was  just  right. 

Ingot  Molds,  Stools  and  Cars.  —  The  arrangement  of  the  molds 
into  which  the  ingots  are  to  be  cast  is  shown  in  Fig.  78,  which  also 
gives  the  dimensions  of  molds  commonly  used  for  railroad  rails, 
wire,  and  pipe.  Molds  last  about  100  heats,  after  which  they  are 
so  cracked  inside  that  they  are  with  difficulty  lifted  off  the  solidi- 
fied ingot  of  steel,  and  are  also  very  liable  to  tear  it,  producing 
cracks  which  are  not  easily  welded  up  later  because  they  become 


FIG.   77.  — TEEMING   INTO   MOLDS. 

oxidized  on  the  interior.  A  continuous  series  of  mold  cars  are  fed 
into  the  steel-mill  at  one  end  and  drawn  out,  with  the  ingot  inside, 
at  the  other  end.  They  should  be  heated  so  hot  that  the  palm  of 
the  hand  will  not  bear  the  heat  on  the  outside,  and  are  washed 
inside  with  a  thin  clay  wash  which  prevents  the  liquid  metal  stick- 
ing to  the  cast  iron.  At  the  pouring  platform  they  are  moved 


108 


THE  METALLURGY  OF   IRON  AND  STEEL 


forward  under  the  ladle  by  means  of  a  little  finger,  which  enters  a 
notch  in  the  side  of  the  car  and  is  itself  carried  on  the  rod  of  a 
hydraulic  piston. 

Stripping.  —  As  soon  as  they  can  be  run  out  to  the  stripping 
house/  the  ingots  are  solidified  sufficiently  on  the  outside  for  the 
mold  to  be  removed,  leaving  the  ingot  standing  on  the  car  ready  to 
be  drawn  to  the  rolling-mill.  In  the  majority  of  cases  it  is  only 
necessary  to  place  the  jaws  of  the  stripping  machine  under  the 
lugs  on  the  mold,  raise  it  up  to  a  sufficient  height,  and  then  trans- 


FIG.    78.  —  INGOT   MOLDS,    STOOL   AND    CAR. 

5000-lb.  molds:  7  ft.  high,  15f  in.  square  at  top,  19i  in.  at  bottom;  about  2£  in. 
thickness  of  cast  iron. 

fer  it  to  a  stool  on  a  car  in  the  second  track  of  the  stripping  house. 
Sometimes  the  ingots  do  not  come  out  so  easily,  however,  and  then 
the  plunger  is  rested  on  top  of  the  ingot,  which  is  held  down  by 
the  hydraulic  pressure  as  the  mold  is  drawn  upward.  Most  strip- 
ping machines  are  actuated  by  hydraulic  power,  although  electric 


THE   BESSEMER  PROCESS 


109 


ones  are  common.  The  empty  molds  are  stored  in  the  yard 
until  they  are  sufficiently  cool  to  be  drawn  back  to  the  steel-mill 
for  another  charge,  and  during  the  wait  they  are  washed  inside 
with  clay  water,  which  is  quickly  dried  by  the  heat  of  the  mold. 

Chemistry  of  the  Acid  Bessemer  Process.  —  If  a  stream  of  air  be 
made  to  impinge  upon  a  melted  bath  of  iron,  the  metal  and  im- 
purities will  be  immediately  oxidized,  about  in  proportion  to  the 


FIG.    79.  —  STRIPPING. 

relative  amounts  of  each  present.  We  may  therefore  consider 
the  chemistry  of  the  Bessemer  process  as  a  union  of  the  oxygen 
from  the  tuyeres  with  the  first  element  it  meets,  irrespective  of 
relative  affinity,  and  a  subsequent  attack  upon  these  oxidized 
elements  by  unoxidized  ones  for  their  oxygen.  As  iron  is  the 
predominant  element,  and  as  the  oxides  of  iron  are  readily  reduced, 
they  especially  serve  as  carriers  of  oxygen  between  the  air  and 
other  impurities: 

1.  FeO  +  Mn  =    Fe  +  MnO. 

2.  FeO   +     C  =  Fe    +    CO. 

3.  2  FeO  +   Si  =  2  Fe  +  SiO2. 

In  the  first  part  of  the  blow,  the  oxides  of  carbon  also  suffer 
reduction : 

4.  2CO  +  Si    =   SiO2  +  2  C. 

5.  CO2  +  Si   =  SiO2  +  C. 

6.  CO  +  Mn  =  MnO  +  C. 


110  THE  METALLURGY   OF   IRON  AND   STEEL 

Equilibrium  is  therefore  established  by  the  elements  which 
have  the  greatest  chemical  affinity  for  oxygen  getting  practically 
all  of  that  agent,  either  directly  or  by  robbing  their  neighbors. 
Some  iron  oxide  survives,  however,  because  it  is  so  predominant 
in  amount  that  its  neighbors  cannot  rob  it  before  a  part  of  it  has 
united  with  silica,  which  is  either  formed  by  the  oxidation  of  silicon 
or  else  won  from  the  lining : 

7.  FeO  +  SiO2  =  FeSiO3. 

The  ferrous  silicate  forms  a  slag  with  manganese  silicate,  and 
this  slag  will  dissolve  oxides  of  iron.  Even  after  the  oxide  of  iron 
has  been  absorbed  by  the  slag,  it  may  be  reduced  by  manganese 
and  carbon,  although  not  to  the  same  extent.  Practically  no 
oxygen  of  the  air  escapes  from  the  bath  uncombined,  even  though 
it  has  but  18  in.  of  metal  to  pass  through  and  amounts  to  more 
than  5000  cu.  ft.  per  minute,1  because  the  blast  pressure  is  made 
high  in  order  that  the  air  may  be  broken  up  into  a  fine  spray  of 
bubbles  as  soon  as  it  strikes  the  metal  and  thus  offer  a  large  sur- 
face of  contact  for  chemical  reaction. 

Slag  Formation.  — Manganese  oxide  unites  with  silica: 

8.  MnO  +  SiO2  =  MnSiO8; 

and  it  is  perhaps  for  this  reason  that  manganese,  unless  very  high 
(say  over  2  per  cent.),  is  removed  early  in  the  blow.  The  silicates 
of  iron  and  manganese  dissolve  in  each  other  and  form  a  slag,  and 
this  slag  will  dissolve  large  amounts  of  iron  oxide,  manganese  oxide, 
silica  and  alumina,  the  latter  coming  from  the  vessel  lining.  At 
all  times  the  bath  is  so  violently  agitated  that  the  metal  and  slag 
are  intimately  mixed,  and  the  reducing  effect  of  manganese,  sili- 
con and  carbon  on  the  iron  oxide  dissolved  in  the  slag  limits  it  in 
amount.  The  slag  itself  therefore  serves  as  a  carrier  of  oxygen 
to  the  impurities. 

Critical  Temperature.  —  As  the  temperature  rises,  chiefly  on 
account  of  the  oxidation  of  silicon,  the  chemical  affinity  of  carbon 
for  oxygen  increases  relatively  more  than  that  of  the  other  im- 
purities, and  reaction  No.  4  ceases  and  then  reverses: 

9.  SiO2  +  2C  =  2  CO  +  Si. 
What  the  critical  temperature  of  this  reversal  is  has  never  been 

1  Air  is  composed  of  20.8  parts,  by  volume,  of  oxygen  and  79.2  parts  of 
^nitrogen,  and  the  amount  of  blast  per  minute  is  15,000  to  30,000  cu.  ft. 


FIG.   80. —  SOAKING   PIT   HEATING   FURNACES   AT   ROLLING   MILL   WHICH 
RECEIVE   THE   RED   HOT,   NEWLY  STRIPPED    INGOT. 


FIG.    81.  — LINE    OF   COOLING    INGOT    MOLDS    OUTSIDE    BESSEMER   MILL. 


112 


THE  METALLURGY  OP  IRON  AND  STEEL 


determined,  but  we  may  estimate  it  as  being  somewhere  between 
1450°  and  1550°  C.  (2642°  to  2822°  F.),  and  unless  the  silicon  is 
all  oxidized  before  this  temperature  is  reached,  we  shall  have 
'residual  silicon'  in  the  steel.  In  English  Bessemer  practice, 
where  silicon  is  often  above  2  per  cent,  of  the  pig  iron,  this  is  not 


3.00  % 


2.00% 


LOO  % 


Carbon 


Metal 


Acid  Bessemer  Blow 
American  Practice 


S, 


0        123456789      10 

Minutes  of  Blowing  End  of  Blow 

FIG.  82. 

rare,  because  the  high  silicon  takes  longer  to  go  and  also  increases 
the  temperature: 

10.  Si  +  20  =  SiOa     (generates  180,000  calories)1. 

1  It  is  immaterial  from  the  heat  standpoint  whether  oxidation  takes  place 
directly  or  as  a  result  of  two  reactions: 

2  Fe     +  2O  =  2  FeO  (generates  131,400  calories) 

2FeO  +  Si  =SiO  +  2Fe      (        "  48,600        "      ) 


180,000 


THE   BESSEMER  PROCESS 


113 


There  is  also  a  critical  temperature  for  manganese  oxidation, 
above  which  reaction  No.  6  is  reversed  and  residual  manganese  is 
left  in  the  steel ;  but  this  happens  only  when  the  manganese  in  the 
pig  iron  is  very  high.  No  warning  is  given  that  the  temperature 
is  approaching  these  critical  points,  because  no  flame  —  nothing 
but  sparks  —  comes  from  the  mouth  of  the  converter  until  carbon 
begins  to  burn,  and  therefore  no  indication  is  given  to  the  operator 
of  the  degree  of  heat  until  too  late. 

Second  Period.  —  The  second  period  begins  when  the  carbon 
commences  to  burn,  which  happens  in  America  only  after  the 


50* 
40* 
30* 
20* 

^^ 

* 

s 

"y 

1701 

Ibs. 

/'* 

g 

^ 

<, 

/ 

/ 

A 

/ 

/ 

S 

ag 

/ 

/ 

/ 

5001 

s. 

x/ 

^? 

''liW 

Ibs. 

// 

- 

.^ 

^MOOlb 

3. 

S* 

4 

V/M 

anganese 

Oxidi 

X* 

' 

f»' 

.-— 

"" 

/ 

"t 

/IK 

Olbs 

|\ 

/ 

J 

/ 

\ 

/10 

XHbi 

N^ 

i 

/ 

\ 

\ 

\ 

JO, 

11234       56789      10 
Minutes  of  Blowing                        End  of  Blow 

FIG.  83. 


silicon  and  manganese  have  been  almost  eliminated,  as  shown  by 
Tables  XIII  and  XIV  and  Figs.  82  and  83.  During  this  period  the 
reactions  consist  principally  of  the  oxidation  of  carbon,  although 
a  little  silicon  passes  off  at  the  same  time.  Further  details  will  be 


TABLE     XIII.— REMOVAL     OF    IMPURITIES    IN    THE    BESSEMER    CONVERTER, 
WITH  ACCOMPANYING  SLAG-ANALYSES 


TIME  AFTER 
COMMENCE- 
MENT OF 
BLOW 

REMOVAL  OF  METALLOIDS  — 
PER  CENT. 

Authority  * 

ANALYSIS  OF  CORRESPONDING  SLAGS  —  PER  CENT. 

c 

Si 

Mn 

P 

S 

O 
n 

q 
3 

1 

0 

£ 

§<s 

$ 

o 

c 

O 

6 

1 

p 

S 

Alkalies 

Min.     Sec. 
Pig  iron. 
2           0 
3         20 
6           3 
8           8 
9         10 
Steel. 
9         20 

Pig  iron. 
8           0 
15           0 
17           0 
18           0 
Steel. 

Pig  iron. 
After  slagging 
End  of  boil. 
End  of  blow. 

Pig  iron. 
3           0 
4         45 
5         45 

Pig  iron. 
2         15 
4         30 
5           0 

Pig  iron. 
3           0 
5           0 
5         45 

Pig  iron. 
2         30 
5         30 
6         30 

Pig  iron. 
4         15 
8         35 
9         20 

Pig  iron. 
3           0 
6           0 
9           0 
12           0 
14         30 
16         30 

2.98 
2.94 
2.71 
1.72 
0.53 
0.04 

0.45 

3.55 
3.21 
1.25 
0.207 
0.034 
0.370 

3.93 
2.465 
0.949 
0.087 

4.00 
4.30 
0.90 
0.10 

3.94 
4.20 
1.10 
0.05 

4.49 
3.87 
1.30 
0.33 

4.35 
4.10 
1.00 
0.08 

4.22 
4.20 
1.30 
0.55 

3.5 
3.6 
3.4 
2.4 
0.09 
0.075 
0.0 

0.94 
0.63 
0.33 
0.03 
0.03 
0.02 

0.038 

2.39 
1.08 
0.11 
0.06 
0.04 
0.06 

1.96 
0.443 
0.112 
0.028 

1.02 
0.03 
0.03 
0.03 

1.14 
0.04 
0.03 
0.01 

1.08 
0.03 
0.03 
0.02 

0.88 
0.10 
0.05 
0.04 

1.06 
0.43 
0.12 
0.07 

1.70 
0.80 
0.28 
0.05 
0.01 
0.0 
0.0 

1.43 
0.09 
0.04 
0.03 
0.01 
0.01 

1.15 

0.49 
0.15 
0.13 
0.13 
0.10 
1.17 

3.46 
1.645 
0.429 
0.113 

1.83 
0.22 
0.12 
0.09 

0.64 
0.12 
0.12 
0.06 

0.83 
0.11 
0.09 
0.07 

1.15 
0.15 
0.15 
0.08 

5.12 
3.26 
0.85 
0.43 

0.100 
0.104 
0.106 
0.106 
0.107 
0.108 

0.109 

0.09 

6.'09 
0.08 

6.09' 

0.040 
0.040 
0.045 
0.045 

0.06 
0.06 
0.06 
0.06 
0.06 
0.06 

0.059 

Howe. 
40  American  39 

42.40 
50.26 
62.54 
63.56 

5.63 
5.13 
4.06 
3.01 

40.29  4.36 
34.24  0.96 
21.26  1.93 
21.39  2.63 



6.54 
7.90 
8.79 
8.88 

1.22 
0.91 

0.88 
0.90 

0.36 
0.34 
0.34 
0.36 

0.008 
0.008 
0.010 
0.014 

0.009  
0.009  
0.014!  
O.OOSi  



62.20 

.276 

17.44 

2.90 



13.72 

0.87 

0.29 

0.010 

0.011 



A12O3 
&P205 

0.018 
trace 

*§ 

.S.2 
Wfc 

1 

H 

44 

t! 

W3) 
c 
W 

Is 

oM    . 

1* 
.Is 

•Bit 

J50 

Is 

•5* 
^ 

OQ 

4 

$$ 

J* 
•&» 

*j» 

*|! 

ms 

.2* 

i 

62.65 
73.24 
75.63 
61.30 
64.15 

40.95 
46.78 
51.75 
46.75 

50.20 
55.26 
47.20 
40.50 

46.50 

48.76 
59.82 
48.48 

51.00 
53.44 
57.80 
55.76 

47.16 
53.26 
62.34 
44.52 

46.72 
45.87 
39.07 
37.63 

7.98 
4.51 
5.19 
4.24 
5.71 
A1208 

8.70 
4.65 
2.98 
2.80 

3.86 
2.86 
2.70 
2.24 

12.90 
0.78 
0.98 
0.72 

2.56 
1.84 
1.94 
1.58 

5.83 
2.28 
3.90 
2.14 

4.36 
3.08 
2.49 
2.94 

1.93 
0.00 
0.00 
13.47 
13.95 

0.60 
6.78 
5.50 
16.86 

1.80 
14.20 
18.52 
31.19 

0.90 
34.72 
21.08 
35.82 

0.90 
20.24 
17.04 
18.48 

0.77 
13.50 
9.54 
30.60 

0.70 
4.20 
6.24 
9.45 

'.'.'.'. 

10.52 
8.72 
7.70 
9.12 
2.39 

15.78 
11.83 
10.92 
10.82 
12.81 

2.18 
37.00 
37.90 
32.23 

5.44 
26.31 
31.01 
25.43 

0.58 
13.95 
15.48 
12.29 

3.40 
23.90 
22.80 
22.23 

2.14 
29.76 
23.70 
21.39 

11.16 
46.38 
52.26 
48.92 

0.65 
1.11 
0.96 
0.75 
0.75 

30.35 
2.98 
1.76 
1.19 

27.22 
0.62 
0.38 
0.32 

32.07 
2.60 
3.25 
2.35 

31.80 
0.44 
0.46 
0.36 

21.79 
0.42 
0.60 
0.38 

19.10 
1.26 
0.70 
1.00 

0.52 
0.64 
0.38 
0.29 
0.24 

16.31 
1.53 
0.45 
0.52 

10.88 
0.22 
0.14 
0.11 

6.75 
0.24 
0.30 
0.21 

9.03 
trace 





..... 

0.01 
0.03 
0.02 
0.01 

0.34 
0.04 
trace 

0.32 
trace 

,... 

::::: 



::::: 

:  :  :  :  : 

:::: 

::::: 

22.18 
0.23 
0.28 
0.21 

18.37 
0.54 
0.29 
0.46 

.!... 











'.'.'.'.'. 



1.50 
1.50 
1.63 
1.43 
1.42 
1.20 
0.08 

0.05 
0.05 
0.05 
0.05 
0.05 
0.05 
0.05 

P2Cv 

32.6 
42.6 
36.0 
35.6 
33.0 
15.6 

7.26 
2.57 
5.91 
6.17 
7.89 
13.43 

0  60 

•••••• 

0  15 

'.'.'.'.'. 

::::: 

••••• 

::::: 

1.60 
2.61 
5.66 
15.06 



::'.:'. 

*  See  No.  52,  page  125. 


THE  BESSEMER  PROCESS 


115 


TABLE    XIV. —  REMOVAL    OF    IMPURITIES    IN    THE    BESSEMER 

PROCESS 


TIME 

AFTER 

COM- 
MENCE- 
MENT 
OF  BLOW 

REMOVAL  OF  METALLOIDS  —  PER  CENT. 

References  and  Remarks 

C 

Si 

Mn 

P 

S 

Min.     Sec. 
Pig  iron  . 
5       0 
10       0 
15       0 
20       0 
25       0 

Pig  iron  . 
5       0 
10       0 
15       0 
20       0 
25       0 

Pig  iron. 
4     30 
13       0 
16       0 
Steel...  . 

Pig  iron  . 
6       0 
12       0 
18       0 
Steel.... 

Pig  iron. 
6       0 
9       0 
13       0 
Steel.... 

Pig  iron  . 
5       0 
10       0 
15       0 
20       0 
25       0 

Pig  iron  . 
5       0 
10       0 
15       0 
18      0 

Pig  iron  . 
4     30 
9     15 
11     15 
13       0 

3.52 
3.6 
3.3 
2.5 
1.0 
trace 

3.5 
3.6 
3.3 
2.5 
1.0 
trace 

3.52 
2.78 
0.43 
0.05 
0.23 

3.57 
3.95 
1.64 
0.19 
0.37 

3.270 
2.170 
1.550 
0.097 
0.519 

3.5 
3.6 
3.3 
3.25 
2.0 
trace 

3.50 
3.55 
2.35 
0.07 
trace 

2.97 
2.480 
0.811 
0.049 
0.0 

3.00 
2.0 
1.25 
0.75 
0.65 
0.35 

3.0 
1.75 
1.25 
0.9 
0.7 
0.5 

1.85 
1.21 
0.93 
0.28 
0.27 

2.26 
0.95 
0.47 

trace 
a 

1.952 
0.795 
0.635 
0.020 
0.033 

2.25 

1.0 
0.5 
0.2 
0.1 
trace 

1.50 
0.50 
0.09 
trace 

1.25 
0.60 
0.20 
0.10 
trace 

German  method.  "Leav- 
ing    Silicon     in     the 
Bath,"     Stahl    und 
Eisen,    vol.     iii,     pp. 
262-264. 

German  method.    Same 
reference. 

German   method.     Carl 
Rott.     31 

j 

English    method.     Carl 
Rott.     31 

English  method.  Snelus. 
See    Encyclopaedia 
Britannica,       Ameri- 
can ed.,  vol.    xiii,  p. 
334. 

.Stahl    und    Eisen,    vol. 
iii,  pp.  262-264. 

["Basic    Process,"  Stahl 
\     und     Eisen,   vol.     iii, 
pp.  262-264. 

"Basic      Process,"     by 
Muller,      at      Horde, 
Encyc.  Brit.,  p.  346. 

0.75 
0.25 
trace 

1.93 
1.69 
1.00 
0  37 

0.62 

0.04 
trace 

u 
0.54 

0.086 
trace 

u 

1C 

0.309 

1.0 
0.35 
0.2 
trace 

0.048 
0.051 
0.064 
0.067 
0.053 

0.014 
trace 

u 
u 
u 

0.71 
0.56 
0.27 
0.12 
trace 

0.61 
0.247 
0.0 
0.0 
0.123 

1.57 
1.60 
1.43 
1.22 
0.08 

1.22 
1.250 
1.320 
0.786 
0.021 

0.16 
0.14 
0.13 
0.12 
0.10 

0.15 
0.206 
0.262 
0.262 
0.206 

0.53 
0.009 
0.0 
0.0 
0.0 

116 


THE  METALLURGY   OF   IRON  AND   STEEL 


teamed  from  the  tables  and  figures.  It  is  interesting  to  note  that 
the  phosphorus  and  sulphur  in  the  metal  are  not  eliminated,  be- 
cause the  acid  slag  will  not  dissolve  them  even  if  they  become 
oxidized.  For  this  reason  the  percentage  of  these  impurities  in- 
creases slightly  during  the  blow,  because  their  actual  weight 
remains  the  same,  while  the  weight  of  the  bath  decreases. 

TABLE  XV.  —  ANALYSES  OF  BOTTOM-BLOWN  CONVERTER-GASES 


TIME  AFTER 

PEJ 

t  CENT. 

STARTING  BLOW 

CO 

CO2 

O 

H 

N 

Reference  * 

2  min 

10  71 

0.92 

88.37 

3  95 

8.59 

0.88 

86.58 

fi    " 

4  52 

8  20 

2  00 

85  28 

Sir  Lothian 

10    "    
12    " 

19.59 
29  30 

3.58 
2  30 



2.00 
2  16 

74.83 
66.24 

Bell.  37 

14    " 

31   11 

1  34 

* 

2.00 

65.55 

18    "    
3  to    5  min 

End  of 

blow. 
9  127 

4.762 

86.111 

1 

9  to  10    "     ... 
21  to  23     "    ... 
26  to  27    "    ... 

2  to    3  min 

17.555 
19.322 
14.311 

5.998 
4.856 
1.853 

6  608 

1.699 
0.967 
0.550 

7  256 

0.908 
1.120 
1.699 

73.840 
73.735 
81.587 

86.137 

Y38 
) 

1 

8tolO    "     ... 
12  to  15     "    ... 
17tol9     "     ... 

15.579 
25.580 
25.606 

5.613 
4.144 
2.995 

1.296 
0.980 
1.318 

1.112 
1.040 
1.120 

76.400 
68.256 
68.961 

jaa    ' 

*  See  No.  52. 

Gases.  —  In  connection  with  Table  XV  it  is  interesting  to  note 
what  a  large  proportion  of  the  carbon  is  oxidized  to  the  monoxide, 
and  this  is  the  more  important  because  this  formation  generates 
only  29,160  calories,  while  the  higher  oxidation  generates  more 
than  three  times  as  much: 

C  +  2  O  =  COa  (generates  97,200  calories). 

Thus  a  large  amount  of  heat  is  wasted,  and  is  generated  only  when 
the  flame  passes  out  of  the  mouth  of  the  converter  and  unites  with 
more  oxygen.  When  the  heat  of  a  charge  is  too  low,  it  is  custom- 
ary at  some  plants  to  tip  the  converter  forward  or  backward,  so 
that  a  few  tuyere  holes  will  be  above  the  level  of  the  bath  and  will 
blow  free  air  into  the  interior  of  the  converter.  This  results  in  a 
portion  of  the  carbon  monoxide  being  oxidized  to  carbon  dioxide 


THE  BESSEMER  PROCESS 


117 


inside  the  converter,  and  is  a  limited  means  of  making  the  blow 
hotter.  Oxidation  of  additional  iron  produces  the  same  effect. 

Slag.  —  In  Table  XIII  the  lime  and  magnesia  in  the  slag  come 
from  a  small  amount  of  blast-furnace  slag  which  finds  its  way  to 
the  converter  through  the  mixer,  in  spite  of  efforts  made  to  hold  it 
back  at  all  points  when  pouring.  Because  the  blast-furnace  slag 
is  basic,  it  has  the  effect  in  the  converter  of  making  the  slags  wet 
and  sloppy,  and  therefore  increasing  the  loss.  Although  the  iron 
as  shot  is  only  shown  in  one  case,  this  is  not  because  it  is  absent 
in  the  other  cases,  but  merely  because  it  was  not  determined.  At 
all  times  the  slag  carries  a  great  many  pellets  of  iron,  which  should 
be  added  to  the  combined  iron,  since  they  represent  a  loss  in  the 
process.  It  is  interesting  to  note  how  closely  the  amount  of  iron 
in  the  slag,  after  adding  the  spiegeleisen,  approximates  15  per 
cent.,1  and  there  seems  to  be  a  chemical  balance  which  fixes  this 
amount  as  a  condition  of  equilibrium.  When  the  silicon  in  the 
pig  iron  is  higher,  and  therefore  the  amount  of  slag  made  is 
'larger,  there  is  a  slightly  lower  percentage  of  iron  oxide  in  it. 
The  practice  of  'side  blowing  for  heating/  described  above,  has 
the  effect  of  increasing  the  amount  of  iron  oxide  in  the  slag  by  in- 
creasing the  oxidizing  influences  in  the  interior  of  the  converter. 
The  rise  in  manganous  oxide  in  the  slag  during  recarburizing 
is,  of  course,  due  to  the  formation  of  MnO  by  the  action  of  the 
manganese  on  the  oxygen  of  the  bath,  while  the  iron  oxide  in 
the  slag  is  reduced  at  the  same  time  by  the  action  of  manganese 
and  carbon. 

The  weight  of  slag  at  different  periods  of  the  Bessemer  process 
has  been  calculated  by  H.  H.  Campbell  2  from  its  analyses,  with 
the  following  average  results: 


TABLE  OF  SLAG  WEIGHTS  IN  BESSEMER  PROCESS 


Percentage  of  blow 
finished 

Pounds  of  slag 

Percentage 
of  charge 

20 

Silicon  flame 

1035 

4.5 

36 

Brightening 

1146 

5.1 

66 

Carbon  flame 

1255 

5.5 

89 

Full  carbon  flame 

1385 

6.1 

1  Not  including  pellets,  which  average  6  to  8  per  cent,  of  the  slag. 

2  See  page  158  of  No.  2.     Old  edition,  1904,  on  page  8  herein. 


118  THE   METALLURGY  OF   IRON   AND   STEEL 

The  final  amount  of  slag  made  will  probably  average  about  7J  to 
8  per  cent,  of  the  weight  of  the  metal  produced,  or,  roughly,  7  per 
cent,  of  the  weight  of  the  pig  iron  charged. 

Flame.  —  A  flame  is  the  result  of  burning  gas,  and  as  practically 
the  only  gas  in  this  process  is  carbon  monoxide,  there  is  no  flame 
except  during  the  period  when  the  carbon  is  burning.  In  the  first 
part  of  the  blow  a  large  number  of  small  sparks  issue  from  the 
mouth  of  the  converter,  consisting  mainly  of  pellets  of  iron  and 
slag  ejected  by  the  blast.  At  the  end  of  the  first  two  or  three 
minutes,  a  small  tongue  of  reddish-yellow  flame  begins  to  pour 
from  the  mouth,  showing  that  the  carbon  is  beginning  to  be  oxi- 
dized. This  soon  increases  in  size  and  brilliancy  until  a  white-hot 
flame,  30  ft.  in  height,  pours  from  the  vessel  with  a  loud  roaring 
sound  caused  by  the  boiling  of  the  bath  and  the  passage  of  the 
blast  and  gas  through  it.  This  boil  lasts  until  the  end  of  the 
operation,  and  the  bath  is  at  all  times  violently  agitated  and  inti- 
mately mixed  with  the  slag,  which  greatly  facilitates  the  reaction 
between  the  two.  The  process  at  this  period  presents  a  spectacle 
which  is  almost  unmatched  as  a  pyrotechnic  display.  Soon  the 
flame  begins  to  flicker  or  'feather'  at  the  edges,  as  a  warning  that 
the  carbon  is  becoming  low,  and  finally  it  shortens  or  drops, 
whereupon  the  converter  is  immediately  turned  down  and  the 
blast  stopped.  The  carbon  at  this  time  will  be  about  0.03  to 
0.10  per  cent.,  depending  on  how  ' young'  or  how  'full'  was  the 
blowing. 

At  all  times  there  is  a  varying  amount  of  slag  and  metal  thrown 
out  of  the  mouth,  so  that  the  converter  may  be  likened  to  a  foun- 
tain of  sparks,  the  great  bulk  of  which  consists  of  slag.  Through- 
out the  blow  there  is  also  a  constant  stream  of  fume  issuing  with 
the  flame.  It  is  a  brownish-red  smoke,  which  rises  to  a  good 
height  and  consists  principally  of  oxide  of  iron  and  manganese. 
Dr.  Charles  F.  Chandler,  Professor  of  Chemistry  at  Columbia  Uni- 
versity, while  observing  this  smoke  at  the  Homestead  steel-works, 
suggested  to  me  that  it  might  be  due  to  the  formation  in  the  bath 
of  iron  carbonyl,  a  volatile  compound  of  iron,  carbon  and  oxygen 
(Fe(CO)5),  and  perhaps  of  manganese  carbonyl. 

Loss.  —  The  difference  in  weight  between  the  pig  iron  charged 
into  the  converter  and  the  steel  ingots  made  will  be  8  per  cent,  in 
good  practice,  although  running  above  that  (say  to  10  per  cent.) 
in  some  mills.  This  is  distributed  as  follows: 


FIG.   84. —  BESSEMER   FLAMES   DURING  A   BLOW. 


120  THE  METALLURGY  OF   IRON  AND  STEEL 

Carbon  burned 3.5  per  cent. 

Silicon  burned 1.0 

Manganese  burned 0.5 

7  per  cent,  slag  @  15  per  cent.  Fe 1.0 

7  per  cent,  slag  @  7  per  cent,  iron  pellets 0.5 

Volatilized  and  ejected 1.5 

8.0        " 

Recarburizing.  —  It  might  be  thought  that  a  more  economical 
method  could  be  found  than  that  of  burning  up  all  of  the  carbon 
in  the  pig  iron  and  then  adding  the  desired  amount,  and  in  fact 
such  a  method  is  employed  in  Sweden,  where  the  carbon  is  burned 
down  to  the  desired  point,  as  estimated  by  the  appearance  of  the 
sparks  issuing  from  the  converter,  the  vessel  being  then  turned 
down  and  the  charge  held  until  a  hammer-test  confirms  this  esti- 
mate. Such  a  complicated  procedure,  however,  requires  a  hotter 
bath  and  very  slow  working,  and  it  is  much  cheaper  to  burn  the 
carbon  until  the  drop  of  the  flame  and  then  add  the  requisite 
amount.  In  making  rail-steel  to  contain  about  0.50  per  cent, 
carbon,  we  will  add  to  15  tons  of  blown  metal  about  3000  pounds 
of  melted  spiegeleisen,  containing  roughly  6  per  cent,  of  carbon, 
12  per  cent,  of  manganese,  and  1.50  per  cent,  of  silicon.  The 
mixture  charged  into  the  spiegel  cupola  for  melting  must  be  higher 
in  manganese  than  this,  as  there  is  a  loss  into  the  cupola  slag  by 
oxidation. 

In  making  dead-soft  steel  for  wire,  material  to  be  welded,  etc., 
we  add  ferromanganese  as  high  in  manganese  as  possible.  This 
material  will  contain  about  7  per  cent,  of  carbon,  80  per  cent,  of 
manganese,  and  13  per  cent,  of  iron.  It  is  only  necessary  to  add 
about  500  pounds  to  a  15-ton  bath,  and  therefore  it  will  dissolve 
without  being  melted,  although  it  is  customary  to  heat  it  to  a  red 
heat  in  order  to  lessen  the  chilling  of  the  metal.  This  dead-soft 
material  will  then  have  the  requisite  amount  of  manganese,  but 
will  be  low  in  carbon  and  frequently  less  than  0.01  per  cent,  in 
silicon.  It  is  not  improbable  that  pure  manganese  metal,  if  it 
were  readily  obtainable,  would  be  used  in  many  cases  instead  of 
ferromanganese,  in  order  that  the  carbon  might  be  still  lower. 
Ferromanganese  and  spiegeleisen  are  made  in  the  blast  furnaces 
by  smelting  very  high  manganese  ores  in  a  manner  somewhat  simi- 
lar to  the  smelting  of  pig  iron. 

Calorific  Equation  of  the  Acid  Bessemer  Operation.  —  The  pre- 
dominant part  that  silicon  plays  in  furnishing  heat  for  the  acid 


THE  BESSEMER  PROCESS  121 

Bessemer  process  is  shown  by  a  calorific  calculation.  In  making 
this,  let  us  assume  that  we  have  a  charge  of  pig  iron  weighing 
30,000  lb.,  and  that  we  burn:  silicon  =  1.00  per  cent.  ;  manganese  = 
0.40  per  cent.;  carbon  =  3.  50  per  cent.;  iron  =  2.00  per  cent.  And 
let  us  assume  further  that  the  average  temperature  during  the 
operation  will  be  1500°  C.,  and  that  the  atmosphere  is  at  0°  C. 
Then: 


Si    +     2O  =  SiOa  produces  ..................     1,900,000 

28.4       2X16 

300  lb.!+  338  lb.  =638  lb. 

338  lb.  of  oxygen  =1470  lb.  air. 

Specific  heat  air  =0.268  cals.  per  lb. 

1470  lb.X!500°  C.X0.268  =  ...............        591,000 

-  -  -  1,309,000 
Mn     +     O  =MnO  produces  ................         198,000 

55  16 
120lb.2+35lb.  =155lb. 

35  lb.  oxygen  =152  lb.  air. 
152  Ib.X  1500°  C.XO.  268=  .................          61,000 

-    137,000 

C         +         O.  =CO  produces  ...............  2,552,000 

12  16 

1050  lb.  +  1400  lb.  =2450  lb. 
1400  lb.  oxygen  =6087  lb.  air. 

6087  lb.  X15000  C.  X0.268  =  ................  2,447,000 

-  -  -  -   105,000 
Fe      +      O  =FeO  produces  ................  704,000 

56  16 

6001b.  +  1711b.  =771  lb. 

171  lb.  oxygen  =743  lb.  air. 

743  lb.  X  1500°  C.  X0.268  =  .....  .  ...........        299,000 

-  •  -   405,000 

Total  net  heat  from  chemical  reactions  =  1,956,000 

1  30,000  lb.  X  1  per  cent.=  300  lb. 

2  30,000  lb.  X  0.40  per  cent.  =  120  lb. 

Now  let  us  suppose  that  the  specific  heat  of  the  metal  is  0.20 
calories,  per  pound,  per  degree  Centigrade;  then  how  many  degrees 
will  it  be  raised  by  the  heat  produced  in  the  chemical  reactions 
of  the  blow? 

30,000  lb.X0.20  cals.  =  6,000  cals.  per  1°  C. 
1,956,000  cals.  H-6,000  cals.  =  326°  C.    Answer. 

This  simple  calculation  neglects  the  heat  lost  by  radiation  through 
the  vessel  lining,  and  the  heat  necessary  to  raise  the  silicon,  man- 
ganese and  carbon  of  the  bath  from  their  temperature  at  the  begin- 
ning of  the  blow,  to  1500°  C.,  and  also  leaves  out  of  account  the 


122 


THE  METALLURGY  OF   IRON  AND   STEEL 


heat  produced  by  the  combination  of  FeO  and  MnO  with  Si02  to 
form  the  slag.  All  these  figures  are  relatively  less  important, 
but  those  who  desire  to  calculate  with  greater  delicacy  should 
consult  J.  W.  Richards'  very  thorough  little  book,  No.  53,  Part 
II,  pages  307-354. 

Basic  Bessemer  Process.  —  The  basic  vessel  is  almost  the  same 
as  the  acid,  except  that  the  lining  is  made  of  calcined  dolomite  held 


3.50 
3.25 
3.00 


10      11      12       13      Umin. 


.2.50 
2.25 
2.00 
1.75 
1.50 


1.00 


CU-T™ 


Mn. 
C 

s 


Fll, 


0        1        2       3       4       5       6       7       8        9      10     11      12      13     Umin. 
FIG.    85.  — REMOVAL    OF    IMPURITIES    IN    BASIC    BESSEMER    PROCESS. 

together  by  about  10  per  cent,  of  tar  and  rammed  in  around  a  pat- 
tern while  still  warm.  In  ramming  up  the  bottom  wooden  pins 
.are  rammed  in  with  the  lining,  and  when  withdrawn  they  leave 
J-in.  tuyere-holes,  through  which  the  blast  enters.  The  object 
of  the  lining  is  to  resist  the  chemical  action  of  the  slag,  and  it  is  not 
desired  to  have  it  enter  in  any  way  into  the  chemical  reaction. 
Before  beginning  the  blowing,  lime  is  added  to  the  bath,  equivalent 
in  weight  to  14  to  20  per  cent,  of  the  iron,  in  order  that  it  may  form 
a  basic  slag,  take  up  all  the  silica  formed,  and  prevent  this  uniting 
with  the  lining. 


THE  BESSEMER  PROCESS  123 

The  basic  blow  is  similar  to  the  acid  one  up  to  the  point  where 
the  carbon  is  eliminated  and  the  flame  drops,  before  which  prac- 
tically no  phosphorus  is  oxidized,  as  its  chemical  affinity  for  oxygen 
is  less  than  that  of  carbon.  The  blow  is  then  continued  for  a  few 
minutes  to  form  what  is  known  as  an  'after-blow/  during  which 
the  phosphorus  is  oxidized  and  absorbed  by  the  basic  slag,  prob- 
ably in  the  form  of  calcium  phosphate,.  There  is  also  an  elimina- 
tion of  sulphur,  at  the  same  time,  although  this  is  never  a  very 
satisfactory  action.  The  indication  given  by  the  flame  during 
the  after-blow  is  not  a  good  guide,  and  the  operation  is  usually 
controlled  by  continuing  the  blow  for  the  given  number  of  minutes, 
or  the  given  number  of  revolutions  of  the  blowing  engine,  after  the 
drop  of  the  flame  which  experience  has  proved  will  produce  the 
desired  dephosphorization.  Before  the  recarburizer  is  added,  a 
sample  of  metal  is  ladled  out  of  the  bath,  quickly  cooled,  and 
broken,  so  that  the  appearance  of  its  fracture  may  be  used  as  a 
final  estimation  of  the  elimination  of  phosphorus. 

Recarburization  of  the  basic  heat  cannot  take  place  in  the 
converter,  because  the  carbon  monoxide  formed  at  this  time  is 
liable  to  reduce  phosphorus  from  the  slag  and  cause  rephosphori- 
zation  of  the  metal.  At  the  end  of  the  blow  the  slag  is  therefore 
poured  off  the  bath  as  completely  as  possible,  and  then  the  rest  is 
held  back  in  the  vessel  when  the  metal  is  poured  into  the  ladle. 
The  amount  of  basic  slag  made  will  be  about  25  per  cent,  of  the 
weight  of  iron  charged  and  will  contain  about  9  per  cent,  of  iron. 
The  loss  of  metal  will  be  much  higher  than  in  the  acid  process, 
averaging  perhaps  13  to  17  per  cent.,  a  part  of  which  is  due  to  the 
fact  that  the  pig  iron  used  contains  a  larger  amount  of  impurities 
to  be  oxidized: 

Carbon , 3.7  per  cent. 

Silicon 0.5         ' 

Manganese 1.5 

Phosphorus 2.5 

25  per  cent,  of  slag  @  9  per  cent.  Fe 2.3 

Pellets 1.0 

Fume  and  ejected 1.5 

13.0      " 

The  demand  for  a  given  composition  of  pig  iron  for  the  basic 
process  is  even  more  rigid  than  for  the  acid  process.  The  silicon 
is  kept  as  low  as  possible  in  order  to  decrease  the  necessary  lime 
addition,  and  also  because  the  combustion  of  phosphorus  is  here 


124  THE  METALLURGY  OF  IRON  AND   STEEL 

relied  upon  to  furnish  the  greater  part  of  the  heat.  The  phos- 
phorus is  not  less  than  1.8  per  cent.,  and  the  manganese  is  high 
in  order  to  aid  in  the  production  of  heat  and  the  elimination  of 
sulphur.  The  calorific  equation  for  fourteen  tons  of  metal  is  shown 
in  Table  XVI. 

TABLE  XVI.  —  CALORIFIC  EQUATION  OF  THE  BASIC  BESSEMER 

PROCESS 
Charge:  30,000  Ib. 

Analysis:  0.50  per  cent,  silicon  burned;  Temperature  of  atmosphere  =0°  C.; 
1.60  per  cent  manganese  Specific  heat  of  air  =0.268  pound- 
burned;  calories  per  1°  C.; 

3.50     per     cent,      carbon       Specific  heat  of  metal  =0.20  pound- 

burned  ;  calories  per  1°  C.  ; 

2.50  per  cent,  phosphorus       Average     temperature     of     blow  = 

burned;  1500°  C. 

3.00  per  cent,  iron  burned; 

Principle  of  calculation  same  as  in  Acid  Bessemer  Operation,  p.  121. 

•p         ^  Surplus 

REACTIONS  oXies        P°und- 

calones         calories 

2  P  +  5  O  =P2O6  produces  ................  4,420;000 

62  80 

750  Ib.   968  Ib. 

4209  Ib.  air  X15000  C.  X0.268  =  ..............  1,  692,000 


Si      +       2O  =SiO2  produces  ................        950,000 

28.4      32 
150  Ib.  169  Ib. 

735  Ib.  air  X  1500°  C.X0.268  =  ..............        295,000 

"   655,000 

Mn       +       O  =MnO  produces  ................        794,000 

55  16 
480  Ib.     140  Ib. 

608  Ib.  air  X  1500°  C.X0.268  =  ........  .  .....  .        244,000 

C.         +        O  =CO  produces  .................      2,552,000 

12  16 

1050  Ib.     1400  Ib. 
6078  Ib.  air  X15000  C.  X0.268  =  ..............      2,447,000 

Fe       +      O  =FeO  produces  ................      1,056,000 

56  16 
900  Ib.     257  Ib. 

1118  Ib.  airX!500°  C.  X  0.268  =  .............        449,000     607,000 

Total  net  heat  from  chemical  reactions  =  4,645,000 

Thus,  much  more  heat  is  generated  in  the  basic  process,  but 
more  is  required  because  a  large  amount  is  absorbed  by  melting 
the  additions  of  lime  to  form  the  basic  slag,  and  also  there  is 
greater  radiation  because  the  blows  are  longer  and  the  operation 
is  slower. 


THE   BESSEMER  PROCESS  125 

The  basic  process  is  much  more  expensive  to  operate  than  the 
acid,  on  account  of  the  longer  time  in  blowing,  delay  at  the  end  of 
the  operation  to  test  for  dephosphorization,  and  greater  cost  for 
repairs,  because  (1)  the  basic  lining  costs  more  than  the  acid,  and 
(2)  it  lasts  but  a  fraction  as  long.  To  balance  this  expense  we 
have  the  much  decreased  cost  for  the  high  phosphorus  pig  iron, 
and  also  the  slight  return  from  the  sale  of  the  slag,  which  is  high 
enough  in  phosphorus  to  be  used  as  a  fertilizer.  The  process  is  no 
longer  operated  in  America,  and  it  seems  improbable  that  it  ever 
will  be  again.  The  high  phosphorus  ores  of  the  Minette  district 
produce  a  pig  iron  which  is,  however,  especially  adapted  to  the 
basic  process,  and  the  skill  of  the  Germans  in  producing  a  high- 
grade  structural  steel  by  this  method,  which  is  the  predominant  one 
in  Germany,  excites  the  admiration  of  the  other  iron  and  steel 
countries. 


REFERENCES  ON  THE  BESSEMER  PROCESS 

See  Nos.  2,  30,  31,  32,  36,  and  the  following  list: 

50.  Richard   Akerman.     "The   Bessemer  Process   as   Conducted 

in  Sweden."  Trans.  American  Institute  of  Mining  En- 
gineers. Vol.  xxii,  1893,  pages  277  et  seq. 

51.  Henry  M.  Howe.     "Notes  on  the  Bessemer  Process."     Jour- 

nal, Iron  and  Steel  Institute,  No.  11,  1890,  pages  100 
et  seq. 

52.  Bradley   Stoughton.     "The    Development    of   the   Bessemer 

Process  for  Small  Charges."  Trans.  American  Institute  of 
Mining  Engineers.  Vol.  xxxiii,  1903,  pages  846  et  seq. 

53.  Joseph  W.  Richards.     "Metallurgical  Calculations."     Part  I, 

Introduction,  Chemical  and  Thermal  Principles,  Problems 
in  Combustion.  1906.  Part  II,  Iron  and  Steel.  1907. 
These  problems  not  only  teach  how  to  calculate  many  very 
important  things  in  connection  with  furnaces  and  their 
efficiency,  but  give  a  good  insight  into  the  principles  of  the 
processes  themselves. 

54.  Friedrich  C.  G.  Miiller.     Untersuchungen  uber  den  deutschen 

Bessemer  process.  Zeitschrift  des  Vereines  deutscher  In- 
genieure.  Vol.  xxii,  1878,  pages  384-404  and  454-470. 


126      THE  METALLURGY  OF  IRON  AND  STEEL 

This  is  one  of  the  most  comprehensive  studies  of  the  metal- 
lurgy of  the  Bessemer  process  in  any  language. 
55.  Hermann  Wedding.  "The  Basic  Bessemer,  or  Thomas, 
Process."  Translated  into  English  by  William  B.  Phillips 
and  Ernst  Prochaska.  New  York,  1891.  This  is  the  fullest 
account  of  the  basic  Bessemer  process. 


VI 

THE  OPEN-HEARTH   OR  SIEMENS-MARTIN   PROCESS 
OPEN-HEARTH  PLANT 

THE  arrangement  of  the  open-hearth  plant  is  not  of  such  vital 
importance  as  that  of  the  Bessemer,  because  the  open-hearth  proc- 
ess is  so  much  slower  that  it  is  easier  to  arrange  the  different 
cycles  so  that  one  will  not  delay  another  and  lessen  the  output  of 
steei.  The  different  open-hearth  cycles  are  as  follows: 

1.  Getting  the  stock  to,  and  in,  the  furnace. 

2.  Supplying  the  furnace  with  fuel  and  air  and  preheating  both 
of  these. 

3.  Working  the  charge,  repairing  the  furnace,  etc. 

4.  Recarburizing. 

5.  Disposing  of  the  steel  and  slag. 

6.  Repairing  and  preparing  ladles,  ingot  molds,  etc. 

A  plan  and  elevation  of  a  typical  open-hearth  plant  is  shown 
in  Figs.  90  and  91.  It  is  not  to  be  presumed  that  all  plants  are 
laid  out  in  the  same  manner,  but  that  shown  is  a  modern  type 
which  is  much  favored  in  America.  The  furnaces  are  arranged  in  a 
long  row,  with  often  as  many  as  ten  in  one  house  and  with  the  level 
of  the  hearth  several  feet  abo>ve  the  general  ground-level  of  the 
plant. 

Melting  Platform.  —  On  the  same  level  as  the  hearth,  and  in 
front  of  the  furnace,  is  the  melting  platform,  or  working  platform, 
upon  which  are  placed  one  or  more  charging  machines,  depending 
upon  the  number  of  furnaces  to  be  served,  running  upon  tracks  ex- 
tending the  entire  length  of  the  working  platform.  The  space 
above  this  is  usually  spanned  by  one  or  more  electric  traveling 
cranes  which  assist  in  repairs  to  the  charging  machines,  in  handling 
materials  on  the  melting  platform,  and  in  pouring  molten  pig  iron 
into  the  furnace  where  such  practice  prevails.  The  melting  plat- 
form has  a  small  extension  around  the  back  of  the  furnace  to  afford 

127 


THE  OPEN-HEARTH  PROCESS 


129 


access  to  the  tap-hole  and  the  ladle  into  which  the  steel  is  poured, 
and  for  putting  the  recarburizer  into  this  ladle  when  necessary. 
Upon  the  working  platform  are  the  valve  handles  for  regulating 
the  admission  of  gas  and  air  to  the  furnace  and  for  reversing  the 
current  of  these  at  the  proper  time. 

Gas  Producers.  —  The  gas  producers  are  situated  outside  of  the 
furnace  house  and  in  a  long  line  parallel  to  it.  This  arrangement 
has  the  great  disadvantage  of  placing  the  men  on  the  working  plat- 


FIG.  92.  — OPEN-HEARTH  MELTING  PLATFORM  AND  CHARGING  MACHINE. 

form  between  the  smoke  of  the  gas  producers  and  the  heat  of  the 
furnace,  but  there  seems  to  be  no  good  way  of  avoiding  it.  As  the 
regenerators  are  usually  placed  underneath  the  working  platform, 
this  situation  of  the  producers  gives  the  least  possible  distance 
which  the  gas  has  to  be  carried,  and  therefore  the  least  possible  loss 
by  deposition  of  tarry  components. 

Stock.  —  The  stock  yards  are  oftentimes  placed  between  the 
furnace  house  and  the  gas  producers,  but  this  nearness  is  not 
necessary  and  stock  is  frequently  stored  by  the  end  of  the  house, 


130 


THE  METALLURGY  OF   IRON  AND   STEEL 


or  even  at  some  distance.  For  its  transfer  to  the  furnace,  the 
stock  is  loaded  into  steel  boxes  similar  to  those  in  Fig.  93.  Three 
or  four  boxes  are  supported  on  a  little  car,  which  is  transferred  in  a 
train  to  the  melting-floor,  passing  over  a  pair  of  scales  on  the  way, 
where  the  weight  is  taken.  Between  the  track  of  the  charging 
machine  and  the  line  of  furnaces  runs  the  track  upon  which  these 
cars  are  transferred,  and  if  a  constant  supply  of  boxes  is  brought 
to  the  machine,  it  can  empty  them  upon  ihe  hearth  of  the  furnace 
at  a  rate  of  about  50  boxes  (equivalent  to  about  125  tons)  per  hour. 


FIG.   93. 

Charging  Machine.  —  A  view  of  a  Wellman  charging  machine 
is  shown  in  Fig.  94.  Its  essential  feature  is  a  long  charging-bar 
with  a  foot  on  the  end  which  can  be  dropped  into  a  socket  on  the 
charging-box.  By  this  means  the  charging-box  is  raised  off  the 
car,  thrust  into  the  open  door  of  the  furnace,  and  turned  upside 
down  to  empty  its  contents  of  pig  iron,  steel  scrap,  limestone,  iron 
ore,  or  other  material,  upon  the  hearth.  The  operator  is  seated  in 
a  little  cage,  which  moves  backward  and  forward  with  the  charging- 
bar,  and  has  within  his  reach  five  levers:  (1)  To  move  the  charg- 


THE  OPEN-HEARTH  PROCESS 


131 


ing-bar  inward  and  outward;  (2)  to  move  the  charging  machine 
backward  and  forward  on  its  track  in  order  to  serve  any  of  the 
furnaces,  or  to  place  itself  opposite  any  of  the  doors  of  a  single 
furnace,  or  to  push  the  train  of  charging-boxes  along  by  means  of 
the  charging-bar;  (3)  to  lock  the  foot  of  the  charging-bar  in  the 
socket  of  the  charging-box ;  (4)  to  raise  the  charging-bar  up  and 
down ;  and  (5)  to  turn  the  box  over. 


FIG.   94. 


Casting-Pit.  —  The  casting-pit  extends  all  the  way  behind,  the 
furnaces;  it  is  on  the  general  ground-level  of  the  plant  and  there- 
fore several  feet  below  the  melting  platform.  This  pit  is  spanned 
by  one  or  more  electric  traveling  cranes  of  large  capacity,  which 
are  used  to  hold  the  ladles  while  the  steel  is  running  into  them  from 
the  tap-hole  of  the  furnace  and  while  it  is  being  teemed  into  the 
ingot  molds.  They  are  also  used  to  serve  the  pit  for  several  pur- 
poses, such  as  carrying  away  the  slag,  transferring  empty  ladles 
to  and  from  the  point  where  they  are  lined  and  dried,  etc.  Through 
the  casting-pit  extend  2  to  4  railroad  tracks.  One  of  these,  and 
sometimes  two,  are  used  for  the  passage  of  the  cars  carrying  the 
ingot  molds,  and  they  therefore  run  along  the  side  of  the  teeming 
platforms  upon  which  the  ladleman  stands  to  pour  the  ingots; 
another  is  used  for  the  railroad  cars  into  which  the  slag,  dirt,  and 
other  waste  material  is  dumped;  and  still  another,  if  present,  is  kept 
clear  for  transfer  purposes. 


132  THE  METALLURGY   OF   IRON   AND   STEEL 


OPEN-HEARTH  FURNACE 

The  form  and  dimensions  of  a  modern  50-ton  rolling  open- 
hearth  furnace  is  shown  in  Figs.  95  to  97.  It  consists  of  a  long 
shallow  hearth  suitably  enclosed  in  fire-brick  and  bound  together 
with  steel,  and  can  be  rolled  forward  in  order  to  pour  material 
out  of  the  tap-hole.  A  stationary  furnace  is  shown  in  Fig.  100. 
There  are  more  stationary  than  tilting  furnaces,  but  the  general 
principles  of  the  steel-making  operation  are  the  same  in  both. 

Regenerators.  —  With  the  furnace  are  connected  two  pair  of 
regenerators  which  preheat  the  gas  and  air  for  combustion.  The 
internal  volume  of  each  of  these  chambers  is  equal  to  -f  to  -fv 
of  that  of  the  working-chamber  itself.  The  larger  the  chamber 
the  greater  will  be  the  amount  of  heat  intercepted  in  them,  and 
therefore  the  lower  the  temperature  of  the  gases  that  go  to  the 
stack.  The  amount  of  space  actually  occupied  by  the  bricks,  or 
checkerwork,  is  the  important  consideration,  however,  and  this 
should  be  from  5000  to  10,000  cu.  ft.,  total,  for  all  four  regenera- 
tors in  a  50-ton  furnace,  the  capacity  of  the  two  gas  regenerators 
usually  being  less  than  that  of  the  air  regenerators,  because  the 
volume  of  gas  used  is  less  than  that  of  the  air,  and  also  because 
the  gas  does  not  require  to  be  preheated  so  much,  since  it  is  already 
somewhat  warm  from  the  gas  producer.  During  the  operation  of 
the  furnace  more  or  less  slag,  dirt,  and  dust  are  carried  over  with 
the  outgoing  gases.  To  intercept  this  the  slag-pockets  or  dirt- 
pockets  A  A  (Fig.  97)  are  provided ;  but  in  spite  of  them  the  space 
between  the  bricks  of  the  checkerwork  becomes  partially  choked, 
and  for  this  reason,  as  well  as  because  the  deposit  of  dust  makes  the 
surface  of  the  bricks  rough,  the  total  area  between  the  bricks  must 
be  much  larger  than  the  area  of  the  ports,  so  that  the  velocity  of 
the  gas  will  not  be  lessened.  The  furnace  must  be  laid  off  for  re- 
pairs when  the  passages  between  the  bricks  are  choked  by  dirt, 
but,  on  the  other  hand,  the  space  is  limited,  because  the  bricks 
must  be  laid  in  such  a  way  that  the  maximum  amount  of  surface 
shall  be  exposed  and  the  gases  forced  to  the  greatest  possible  con- 
tact with  them.  The  modern  construction  makes  the  regenera- 
tors as  tall  as  possible  in  order  that  incoming  gas  and  air  may  be 
forced  into  the  furnace  by  the  draught,  and  also  because  this  chim- 
ney effect  causes  the  incoming  gas  and  air  to  naturally  seek  the 


Longitudinal  Section  and  Elevation 


Main  Gas  Flue 


*xSf 

i  i        !  i 

H!"—  <4i 

J[  v  iL 

jrt-^^M 

M 

!  **  —  i 

1ist»ckjr 

l'^-'^1 

'      «  '  I         ,T     I  ' 

,--f====-^. ^jcat — A J/x-M  - 

ijiiSl"  "7     1    "x?T?\ 


I — 


-so'o- >] 


p 

n 

"T"I 

Casting  Pit 

Casting  Pit 

| 

• 

FIGS.    95   AND   96. 


134 


THE  METALLURGY  OF   IRON  AND   STEEL 


hottest  places  and  the  outgoing  gas  to  naturally  seek  the  coolest 
places,  in  this  way  equalizing  the  temperature  in  the  different 
parts  of  the  regenerators. 

The  space  underneath  the  checkerwork  should  be  so  large  that 
the  incoming  gas  and  air  will  distribute  itself  nearly  uniformly 
through  the  different  passages,  and  the  temperature  of  the  fire- 


n       n  r-i  n  r-i  n 


FIGS.  97  AND  98. 

bricks  at  this  lower  part  will  be,  say,  400°  C.  (752°  F.),  although 
varying,  of  course,  at  different  furnaces  and  at  different  times. 
When  the  regenerator  is  receiving  the  waste  gas  from  the  furnace, 
the  temperature  of  these  bricks  will  be  that  of  the  gases  that  go  to 
the  chimney,  say  400°  to  600°  C.,  and  when  the  air  or  gas  is  passing 
through  the  regenerator  on  its  way  to  the  furnace,  these  bricks 


THE  OPEN-HEARTH  PROCESS 


135 


will  be  somewhat  cooler,  depending  upon  the  length  of  time  that 
the  regenerator  has  been  in  this  phase  of  the  operation.  The  tem- 
perature of  the  bricks  at  the  top  of  the  regenerator  will  be  about 
1000°  C.  (1832°  F.),  and  therefore  the  air  and  gas  entering  the 
furnace  will  be  the  same. 

Ports.  —  The  ports  are  so  arranged  that  the  flame  shall  be 
deflected  away  from  the  roof  and  yet  not  impinge  upon  the  bath, 
or  impinge  only  very  slightly,  because  the  bath  would  thereby  be 
oxidized  excessively.  The  gas  should  be  spread  out  all  over  the 


FIG.  99.  — REMOVABLE  BUGGIES  TO  CATCH  SLAG  IN  SLAG  POCKETS. 


width  of  the  hearth  beneath  the  air,  and  the  two  should  be  brought 
together  just  before  they  enter  the  laboratory,  or  work-chamber. 
The  air  especially  must  be  kept  away  from  direct  contact  with  the 
bath,  and  for  this  reason  the  gas-ports  are  placed  below  the  air- 
ports, which  arrangement  has  the  further  advantage  of  promoting 
a  better  mixing  of  the  two,  since  the  gas  is  lighter  and  therefore 
rises.  In  America  the  favorite  arrangement  is  two  gas-ports, 
above  which  is  situated  a  long  slit,  extending  almost  the  entire 
width  of  the  furnace,  which  serves  as  an  air-port.  This  is  not  uni- 
versal practice,  however,  for  in  some  cases  there  are  two,  or  even 
three,  air-ports.  In  one  case  the  two  gas-ports  are  built  wide  and 
low,  so  that  they  will  deliver  thin  streams  and  get  a  better  mix- 


136  THE  METALLURGY  OF   IRON  AND   STEEL 

ing  of  the  two  materials  for  combustion.  The  area  of  the  air-port 
in  a  50-ton  furnace  should  be  about  18  sq.  ft.,  and  the  combined 
area  of  all  the  gas-ports  on  one  end  should  be  from  8  to  10  sq.  ft., 
depending  upon  the  quality  of  gas  used. 

The  roof  must  be  protected  from  the  direct  impact  of  the  flame, 
because  even  the  most  refractory  silica  bricks  would  be  melted  by 
the  intense  heat.  The  heat  in  the  regenerators  and  uptakes  gives 
the  gas  and  air  a  velocity  which  causes  them  to  enter  the  furnace 
with  some  force,  and  the  construction  of  the  ports  directs  the  stream 
in  the  desired  manner.  The  mouths  of  the  ports  are  gradually 
melted  away  by  the  intense  heat  of  combustion  of  the  outgoing 
gases,  until  they  finally  cease  to  serve  this  purpose  and  it  is  im- 
possible to  get  the  proper  mixing  and  the  proper  kind  of  a  flame  in 
the  laboratory  of  the  furnace.  The  ports  must  then  be  repaired, 
else  the  temperature  cannot  'be  maintained. 

Draught  and  Chimney.  —  The  draught  must  be  sufficient  to  catch 
the  flame  about  in  the  middle  of  the  laboratory  and  drag  it  out 
through  the  ports  on  the  opposite  side  from  which  it  entered  with- 
out allowing  it  either  to  drop  down  and  touch  the  bath  (as  this  is  to 
be  heated  almost  altogether  by  radiation)  or  to  impinge  upon  the 
roof.  This  draught  also  has  to  do  the  work  of  overcoming  the  fric- 
tion of  the  outgoing  regenerators  and  flues.  Its  force  will  depend 
upon  the  height  of  the  chimney  and  the  temperature  of  the  products 
•  of  combustion  after  they  have  left  the  regenerators,  which  should 
be  about  400°  C.  (752°  F.),  though  even  better  economy  (i.e.,  a 
lower  temperature)  than  this  is  obtained  in  many  cases.  All  the 
heat  carried  away  by  these  flue  gases  is  of  course  wasted,  but  the 
very  great  cost  of  the  refractory  bricks  in  the  regenerative  cham- 
bers makes  it  unwise  to  reduce  the  temperature  of  the  flue  gases 
too  much  by  enlarging  the  checkerwork.  The  calculation  of  the 
amount  of  draught  produced  by  any  given  height  of  chimney  with 
any  given  temperature  of  flue  gases,  according  to  the  method  of 
Professor  J.  W.  Richards,  is  given  in  Table  XVII. 

Roof.  —  The  roof  is  made  very  thin  and  of  the  most  refractory 
bricks  that  can  be  obtained,  i.e.,  almost  pure  silica,  with  enough 
lime  to  hold  it  together  in  a  compact  mass.  The  walls  are  also 
thin,  and  the  radiation  from  the  furnace  chamber  is  great,  but 
this  has  to  be  endured,  as  thicker  walls  and  roof  produce  endless 
trouble  by  expansion  and  contraction.  The  roof  is  arched  and 
"  suspended  from  beams  independent  of  the  side  walls. 


THE  OPEN-HEARTH   PROCESS  137 


TABLE  XVII.  —  CALCULATION  OF  DRAUGHT  OF  CHIMNEYS 

The  draught  in  a  chimney  is  produced  by  the  gases  within  it  being  lighter 
than  the  air  outside,  and  this  lightness  is  due  to  their  being  hotter.  In  this 
calculation  we  assume  the  following  data: 

Air  weighs  1.29  oz.  per  cu.  ft.  at  0°  C.  and  760  mm.  pressure; 
Chimney  gases  weigh  1.03  times  air  at  0°  C.  and  760  mm.  pressure; 
Data       Water  weighs  772  times  air; 
assumed    Mercury  weighs  13.6  times  water; 

The  friction  of  a  chimney  absorbs  the  equivalent  of  0.1  in.  of  water 
on  a  water-gauge  showing  draught,  for  every  100  ft.  height 
of  chimney. 

As  the  gases  rise  in  the  chimney  they  cool;  therefore  their  average  tempera- 
ture will  be  about  50°  C.   cooler  than  their  temperature  at  the  foot  of  the 
chimney.     Call  this  average  temperature  T°  C.     Then: 
9700  /^ 

1.29  oz.  X  1.03  X  —          — =  the  weight  of  a  cu.  ft.  of  the  chimney  gases 

T°  C.  +  273°  C.         at  the  temperature  T°  C. 

Subtract  this  weight  from  1.29  oz.  and  we  get  the  difference  in  weight  of  air 
and  the  furnace  gases  at  the  temperature  T°  C.  Then: 

Height  of  chimney  X  difference  in  weight  =  ounces  draught  pressure  per  square 

foot  of  chimney  area. 

Ounces^draught  X  12  in.  =  equivalent  height  of  a  water-gauge. 

From  the  height  of  a  water-gauge  so  found,  we  must  subtract  the  amount 
lost  by  friction,  or  0.1  in.  Xheight  of  chimney -7- 100. 

For  further  modifications  of  this  type  of  calculation  see  No.  53,  Part  I,  pp. 
164,  166,  194,  200,  and  201. 

Life  of  the  Furnace.  —  The  '  life'  of  an  open-hearth  furnace 
means  the  number  of  heats  that  it  can  make  continuously  without 
stopping  for  any  more  extensive  repairs  than  can  be  made  in  the 
usual  week's-end  shut-down.  No  figure  can  be  given  for  this 
except  in  the  most  general  way.  The  life  of  the  furnace  will  be 
ended  usually  in  one  of  three  ways:  (1)  The  falling  in  of  the  roof, 
(2)  the  eating  way  of  the  ports,  so  that  the  flame  can  no  longer  be 
maintained  properly,  or  (3)  the  giving  out  of  the  regenerators, 
which  may  occur  either  through  the  choking  of  the  checkerwork, 
or  through  a  crevice  formed  by  the  contraction  and  expansion  of 
the  bricks,  so  that  there  is  a  serious  leak  between  the  gas-chamber 
and  the  air-chamber,  and  premature  combustion  takes  place.  If 
a  basic  furnace  makes  350  heats,  it  is  considered  good  work,  and  we 
may  perhaps  tentatively  consider  this  figure  as  the  "three-score 
years  and  ten"  of  a  furnace  making  steel  for  structural  work  and 
similar  purposes.  Three  hundred  and  fifty  heats  would  mean 


138 


THE   METALLURGY  OF   IRON   AND   STEEL 


about  18  to  24  weeks'  work  in  America.     An  acid  furnace  will  last 
about  1,000  heats. 

Construction  of  Hearth  and  Bottom.  —  The  hearth  is  made  with 
a  thickness  of  18  to  24  in.  inside  the  furnace  shell,  in  the  form  of  a 
shallow  dish  whose  sides  reach  up  to  the  level  of  the  charging  doors, 
and  so  constructed  that  the  depth  of  the  metal  will  be  from  12  to 
24  in.  —  the  former  figure  in  the  case  of  a  very  small  furnace,  say  5 
to  15  tons,  and  the  latter  in  the  case  of  one  of  50-ton  capacity.  If 
the  bath  is  too  shallow  the  oxidation  will  be  excessive  and  the 
wear  of  the  lining  by  oxide  of  iron,  with  consequent  production 

It  is  now  considered  best  to  have 
a  12  *  roof  through-out 


=  1  Course  chrome  brick' 
Silica  brick 


^These  checker  brick 
rest  on  tile  18  x  12  xt 


Silica  brick  from  hen  i 


clay  brick  below  line 


|4  __  Loam,  fettling  etc. 


2  Courses  magnesite  brick  on  edge 
1  Course  chrome 


Granite  or  concrete 


These  checkers  are  not  in  the 
uptake  but  in  a  chamber  just 
beyond  and  opening  into  in. 


FIG.  100.  —  MATERIALS    OF   CONSTRUCTION   AND   LINING   FOR   BASIC 
OPEN-HEARTH    FURNACE. 

of  slag,  will  be  great;1  if  the  bath  is  too  deep,  the  melting  and 
oxidation  will  be  slow.  In  the  case  of  an  acid  bottom,  that  portion 
of  the  lining  next  to  the  shell  will  be  made  up  of  refractory  clay 
brick,  and  the  upper  portion  will  be  formed  by  shoveling  in  silica 
sand,  spreading  it  out  in  a  thin  layer  about  ^  in.  thick  over  the 
entire  hearth,  and  then  allowing  it  to  sinter  at  the  full  heat  of  the 
furnace  for  about  ten  minutes,  so  as  to  set  it  firmly  in  place. 
Upon  this  layer  will  be  set  another  layer  in  like  manner,  until 
the  whole  hearth  is  constructed,  and  then  it  will  be  'washed'  with 

1  In  an  open-hearth  furnace  the  lining  suffers  the  greatest  wear  at  the 
side  of  the  bath,  where  it  is  thin,  because  the  oxidation  of  the  metal  is  the 
greatest  there. 


THE  OPEN-HEARTH  PROCESS  139 

a  melted  bath  of  old  slag  to  fill  up  all  crevices  and  give  a  glazed 
surface. 

In  the  case  of  the  basic  hearth,  the  bottom  is  made  of  calcined 
dolomite,1  held  together  with  10  per  cent,  or  less  of  anhydrous  tar. 
In  this  case  the  layer  of  brick  next  to  the  lining  is  very  thin  and 
the  dolomite  and  tar  are  set  in  in  layers  by  the  heat  of  the  furnace 
as  in  the  case  of  the  acid  lining.  The  tar  burns  to  a  strong  coke, 
which  holds  the  mass  together  in  a  firm  hard  form.  In  some  cases 
no  tar  is  used,  and  the  calcined  dolomite  is  fritted  slightly  to  hold  it 
together;  in  other  cases  15  per  cent,  of  old  slag  is  used  as  a  bond. 
Pure  magnesite  gives  a  more  permanent  lining  than  dolomite,  and 
is  now  much  used  since  its  longer  life  more  than  compensates  for 
its  greater  expense.  Even  when  magnesite  is  used  for  the  bottom, 
the  topmost  layer,  or  working  bottom,  and  the  repairs,  or  'fettling/ 
put  in  during  the  intervals  of  the  furnace  life,  are  made  of  dol- 
omite, because  this  sets  more  quickly.  As  the  sides  and  roof  even 
of  the  basic  furnace  are  made  of  silica  bricks,  it  is  customary, 
although  not  absolutely  necessary,  to  put  a  layer  of  neutral 
material  between  these  bricks  and  the  basic  hearth,  and  also  to 
protect  this  joint  from  excessive  heat.  The  neutral  material 
commonly  used  is  chromite  bricks,  which  are  made  of  ground 
chromite  (FeO,  C^Oa),  held  together  with  tar  and  then  burned 
to  form  a  firm,  hard  mass. 

Repairing  Bottoms.  —  Between  the  heats,  bottoms  are  re- 
paired by  filling  up  holes  with  acid  or  basic  material,  as  the  case 
may  be,  and  by  more  extensive  attention  at  the  end  of  the  week. 
In  this  way  the  bottom  may  be  made  to  last  almost  indefinitely, 
unless  a  part  of  the  charge  works  its  way  down  a  crevice  and 
forces  up  whole  sections  of  the  bottom  lining,  which  not  infre- 
quently happens;  while  sometimes  the  charge  even  works  its  way 
out  through  the  bottom  of  the  furnace.  A  sticky  or  viscous  slag 
is  also  liable  to  bring  the  bottom  up  by  sticking  to  it.  In  the 
tilting  furnace,  the  bottom  may  be  repaired  along  the  point  where 
the  worst  corrosion  usually  takes  place  — Le.,  at  the  edge  of  slag 
line  —  even  during  the  operation,  by  tipping  the  furnace  until 
this  place  is  uncovered. 

Tap-Hole.  —  In  the  stationary  furnace,  the  tap-hole  is  made 
according  to  the  section  in  Fig.  101.  During  the  operation  this  is 

1  Dolomite  is  a  magnesia  limestone,  and  after  calcining  consists  of  a  mixture 
of  lime  and  magnesite  (CaO,  MgO),  with  a  little  silica  and  other  impurities. 


140 


THE   METALLURGY  OF   IRON   AND   STEEL 


closed  by  material  rammed  into  it  from  the  door  of  the  furnace. 
It  sets  quickly  into  a  solid  mass,  which  is  pierced  with  a  pointed 
bar  when  it  is  desired  to  allow  the  metal  to  run  out.  After  tap- 
ping, the  hole  must  be  entirely  freed  from  metal,  and  then  it  is 
made  up  and  filled  anew,  ready  for  the  next  operation.  This 
always  delays  work  to  some  extent,  and  occasionally  the  tap-hole 
causes  trouble  by  the  charge  working  through  it  prematurely,  or, 
on  the  other  hand,  by  its  becoming  so  hard  that  a  hole  is  pierced 
in  it  only  after  a  long  delay  and  much  difficulty,  during  which  the 
oxidation  continues  in  the  charge  beyond  the  desired  point.  In 
the  tilting  furnace  there  is  no  tap-hole,  strictly  speaking,  but  the 


FIG.    101. 


opening  into  the  metal-spout  is  closed  by  loose  material,  which  is 
scraped  away  before  the  furnace  is  tipped  to  pour  the  charge. 

Tilting  Compared  with  Stationary  Furnaces.  —  Tilting  furnaces 
are  more  expensive  to  install  than  stationary  ones,  and  require 
repairs  to  the  machinery  and  power  to  operate  them.  They  also 
require  special  arrangements  of  ports  and  uptakes,  to  be  described 
later,  and  means  for  cooling  the  junction  between  the  movable 
and  stationary  parts  of  the  furnace.  Their  advantages  are  that 
they  do  away  with  troubles  and  delays  from  the  tap-hole,  the 
slag  can  be  poured  off  at  any  time,  and  the  charge  may  be  tapped 
at  a  moment's  notice,  which  is  especially  advantageous  when 
making  steels  within  very  narrow  limits  of  composition.  Further- 
more, the  back-wall  of  the  bottom  may  be  repaired  more  easily 
between  heats  when  the  furnace  itself  is  still  white  hot.  In  the 
stationary  furnace  the  angle  of  this  back-wall  will  be  about  60° 
or  70°  from  the  horizontal,  and  loose  material  thrown  in  from 


THE  OPEN-HEARTH  PROCESS 


141 


the  front  doors  will  not  rest  on  this  angle;  but  the  tilting  furnace 
can  be  tipped  until  the  back-wall  is  more  nearly  horizontal,  and 
then  loose  material  will  remain  upon  it  until  sintered  into  place. 


The  tilting  type  is  of  more  advantage  in  the  basic  process  than  in 
the  acid,  because  it  enables  the  slag  to  be  poured  off  at  will,  which  is 
occasionally  advantageous  in  basic  practice. 


142 


THE   METALLURGY   OF   IRON    AND   STEEL 


Tilting  Furnaces.  —  There  are  two  types  of  tilting  furnaces, 
known  respectively  as  the  Campbell  and  the  Wellman.  In  the 
Campbell  type  the  hearth  of  the  furnace  is  arranged  so  that  the 
center  of  tilting  is  coincident  with  the  center  of  the  ports,  and 
therefore  the  furnace  can  be  oscillated  without  cutting  off  the 
supply  of  gas  and  air.  In  order  to  facilitate  this,  there  is  a  little 
clearance  between  the  uptake  and  the  furnace  proper,  and  these 
parts  are  surrounded  by  water-cooled  castings.  In  the  Wellman 


FIG.    103. —  TILTING   FURNACES. 


type  the  gas  and  air  supply  must  be  cut  off  when  the  furnace  is 
tilted.  In  tipping  the  Wellman  furnace  the  ports  move  with  the 
hearth,  and  they  are  therefore  seated  in  a  water-tank,  which  makes 
an  air-tight  connection  with  the  regenerators  when  the  furnace 
is  in  a  horizontal  position,  but  breaks  it  when  it  is  tipped  forward. 
The  Wellman  type  is  not  as  expensive  to  build  as  the  Camp- 
bell, and  probably  requires  less  repairs.  The  Campbell  type  has 
the  advantage  that  the  bottom  can  be  repaired  along  the  slag  line 
without  interrupting  the  operation,  and  that  the  bottom  can  be 


THE  OPEN-HEARTH   PROCESS 


143 


sintered  into  place  by  the  heat  of  the  flame  when  the  hearth  is  in 
any  position.  This  is  more  important  in  the  acid  furnace  than  in 
the  basic,  where  the  mixture  of  dolomite  and  tar  can  be  set  by 


the  heat  contained  in  the  furnace  walls  themselves.  In  the  Well- 
man  type,  when  the  furnace  is  tipped  for  pouring,  cold  air  can 
enter  it  through  the  port-holes,  and  may  oxidize  the  manganese  in 
the  final  product  after  recarburizing.  Finally,  a  great  advantage 


144  THE  METALLURGY  OF   IRON  AND   STEEL 

of  the  Campbell  type  is  the  fact  that  a  great  deal  of  ore  can  be 
used  during  the  operation,  and  although  the  boiling  of  the  charge 
is  violent  on  this  account,  metal  does  not  flow  out  of  the  furnace 
doors,  because  the  hearth  can  be  tipped  in  the  opposite  direction. 
The  slag  which  runs  off  during  this  period  is  allowed  to  pass 
through  a  hole  in  the  bottom  of  the  port-opening,  at  the  joint  be- 
tween the  fixed  and  the  rotating  portion,  where  it  is  continually 
exposed  to  the  flame  and  therefore  not  liable  to  chill  up. 

Temperature  Calculation.  —  There  is  almost  no  limit  to  the 
temperature  that  can  be  obtained  in  the  open-hearth  furnace  by 
frequent  reversing  of  the  valves,  except  the  danger  of  melting  the 
roof.  The  temperature  is  controlled  by  reversing  and  by  throt- 
tling the  amount  of  gas  and  air  admitted  to  the  furnace.  It  is  the 
almost  universal  practice  to  reverse  the  valves  every  twenty  min- 
utes, in  order  to  maintain  a  uniform  temperature  of  the  regenera- 
tors. Thp  melter  endeavors  to  keep  the  charge  always  in  a  very 
liquid  state,  and  at  the  same  time  to  have  a  slight  excess  of  air,  in 
order  that  the  atmosphere  of  the  furnace  may  be  slightly  oxidizing 
to  burn  the  impurities  in  the  metal.  Every  excess  of  oxygen, 
however,  causes  a  loss  of  heat,  because  each  volume  of  oxygen  in 
the  air  is  accompanied  by  four  volumes  of  nitrogen,  which  carries 
heat  out  of  the  furnace,  but  does  not  assist  in  any  way  in  the  re- 
actions. 

The  actual  temperature  of  the  furnace  will  depend  upon  the 
length  to  which  the  decarburization  is  carried,  because  as  the  metal 
gets  lower  and  lower  in  carbon,  it  requires  a  higher  heat  to  keep  it 
fluid.  It  will  average  about  1600°  to  1700°  C.  (2912°  to  3092°  F.). 
An  operation  which  is  interrupted  when  the  carbon  is  still  0.50 
per  cent,  will  take  much  less  fuel  than  one  in  which  dead-soft  steel 
is  manufactured.  The  amount  of  coal  burned  in  the  gas  pro- 
ducers, per  ton  of  steel  produced,  will  therefore  vary  greatly,  but 
will  average  perhaps  400  to  1000  Ib.  Figures  for  oil  and  natural 
gas  fuel  will  be  given  on  pages  167  and  169. 

Size  of  Open-Hearth  Furnace.  —  The  so-called  '  standard'  open- 
hearth  furnace  has  a  capacity  of  50  tons.  The  bath  in  such  a  fur- 
nace will  have  a  length  of  about  30  to  35  ft.,  a  width  of  about  12  to 
15  ft.,  and  a  maximum  depth  of  about  24  in.  In  America,  how- 
ever, there  is  now  (1907)  a  tendency  to  increase  the  size  to  a 
capacity  of  60  or  even  75  tons.  This  innovation  is  due  largely  to 
Mr.  T.  S.  Blair,  Jr.,  of  the  Lacka wanna  Steel  Company;  some  of  the 


THE  OPEN-HEARTH  PROCESS  145 

furnaces  under  his  control  are  43  ft.  between  the  ports.     The  re- 
sult is  a  much  better  opportunity  for  complete  combustion  within 
the  laboratory  of  the  furnace,  and  therefore  less  deferred  combus-f 
tion  as  the  gases  escape  through  the  ports  and  downtakes.     This 
lengthens  the  life  of  the  ports  and  promotes  fuel  economy. 

The  smallest  practicable  size  of  an  open-hearth  furnace  is  about 
15  tons,  and  this  is  very  expensive  to  operate.  There  are  furnaces, 
however,  as  small  as  5  tons  capacity,  but  this  is  not  good  practice, 
even  under  the  special  circumstances  which  alone  justify  the  use 
of  the  15-ton  furnace.  The  maximum  practical  size  will  not  be 
far  above  75  tons,  and  the  real  governing  factor  is  the  ability  of 
the  mechanical  apparatus  to  handle  the  raw  material  and  the 
product,  besides  which  it  is  difficult  to  cast  so  much  metal  out 
of  one  ladle  without  having  the  casting  temperature  of  the  first 
metal  too  hot,  or  else  that  of  the  last  metal  too  cold. 

BASIC  OPEN-HEARTH  PRACTICE 

Formerly,  the  open-hearth  practice  was  divided  into  two  types, 
known  respectively  as  the  '  pig-and-ore  process7  and  the  '  pig-and- 
scrap  process.7  In  the  pig-and-ore  process  the  charge  consisted 
entirely  of  pig  iron,  and  the  oxidation  was  hastened  by  the  addi- 
tion of  as  much  ore  as  the  charge  would  stand  without  boiling 
over;  in  the  pig-and-scrap  process  the  charge  consisted  of  pig  iron 
with  large  amounts  of  steel  scrap,  the  proportion  of  the  latter  being 
so  large  in  some  cases  that  the  operation  became  a  mere  remelting 
process,  there  being  only  enough  pig  iron  for  its  silicon,  manganese 
and  carbon  to  protect  the  metal  from  excessive  oxidation.  At  the 
present  time  the  pig-and-ore  process  does  not  exist  in  its  original 
form,  but  normal  charges  consist  of  pig  iron  and  steel  scrap,  in  pro- 
portions determined  by  financial  considerations,  and  the  opera- 
tion is  hastened  by  judicious  additions  of  ore.  The  amount  of 
steel  scrap  will  vary  all  the  way  from  0  to  90  per  cent.,  and  will 
average  not  far  from  50  per  cent,  in  America  (1906).  By  decreas- 
ing the  proportion  of  impurities  in  the  raw  material  in  the  charge 
the  scrap  enables  the  process  to  be  completed  in  less  time. 

Charge.  —  A  difference  of  opinion  exists  as  to  whether  it  is 
desirable  to  charge  the  steel  scrap  first  upon  the  hearth  and  then 
cover  it  with  the  pig  iron,  in  order  that  the  impurities  in  the  latter 
may  lessen  the  oxidation  of  iron  during  the  melting  period,  or 


146  THE  METALLURGY   OF   IRON  AND  STEEL 

whether  it  is  better  to  put  the  pig  iron  on  the  hearth  and  cover  it 
with  the  steel,  upon  the  theory  that  the  hearth  is  in  this  way  cor- 
roded less  by  oxide  of  iron.  The  former  practice  is  in  vogue  at 
several  American  works,  and  the  latter  at  some  American  and 
many  English  works.  It  is  probable  that  the  scrap,  unless  small 
in  size,  does  not  corrode  the  hearth  much,  and  the  practice  of  put- 
ting the  pig  iron  on  top  is  preferable.  In  acid  open-hearth  practice 
it  is  more  common  to  charge  all,  or  most,  of  the  scrap  on  top;  in 
basic  practice  we  may  charge,  first  limestone,  then  scrap,  and 
lastly  pig,  or  else,  limestone,  most  of  the  scrap,  most  of  the  pig, 
and  then  a  layer  each  of  scrap  and  pig. 

Composition  of  Pig  Iron  Used.  —  Basic  pig  should  be  free  from 
adhering  sand,  and  therefore  only  machine-cast  metal  will  ordi- 
narily be  used,  or  else  that  cast  in  metal  molds.  Its  silicon  should 
be  below  1  per  cent.,  and  its  manganese  above  1  per  cent.,  though 
the  price  of  manganese  ore  makes  this  ingredient  an  expensive 
luxury.  It  is  desired  because  it  makes  the  slag  more  fluid  and 
aids  in  removing  sulphur.  The  phosphorus  will  be  almost  any 
figure  up  to  2  per  cent.,  but  a  regular  supply  of  pig  with  more 
phosphorus  than  that  would  tempt  the  manager  toward  the  basic 
Bessemer  process.  Silicon  and  phosphorus  increase  the  amount  of 
slag,  lengthen  the  operation,  and  require  lime  to  flux  them. 

Fluxes.  —  The  function  of  the  basic  lining  is  to  remain  inert 
and  serve  simply  as  a  container  for  the  bath.  In  order  that  the 
slag  may  be  at  all  times  rich  in  lime  (35  to  45  per  cent.  CaO  ordi- 
narily), from  5  to  30  per  cent,  of  lime  is  added  with  the  pig  and 
scrap,  the  exact  amount  depending  upon  the  purity  of;  {the  metal 
charged.  Especially  if  the  charge  is  high  in  sulphur,  the  slag  must 
be  kept  as  rich  in  lime  as  possible  without  making  it  too  infusible 
and  therefore  viscous,  the  limit  being  about  55  per  cent.  CaO  in 
this  respect.  The  lime  is  usually  added  in  the  form  of  calcined 
limestone,  and,  as  already  noted,  the  higher  the  silicon  and  phos- 
phorus in  the  metal  the  greater  must  be  the  amount  of  lime  used. 
It  is  also  customary  to  charge  ore  with  the  pig  and  scrap,  in  order 
to  increase  the  amount  of  oxidation  that  takes  place  during  the 
melting.  This  ore  has  very  little  effect  on  the  basic  lining, 
although  it  would  rapidly  corrode  a  silicious  one.  Further  addi- 
tions are  made  during  the  operation  if  necessary.  The  average 
amount  of  ore  added  to  a  50-ton  charge  will  be  between  J  of  a  ton 
and  2J  tons. 


THE  OPEN-HEARTH   PROCESS 


147 


Chemistry.  —  It  takes  about  3  or  4  hours  for  the  charge  to 
melt,  and  during  that  time  the  silicon  is  almost  entirely  eliminated, 


10- 


Hours 


FIGS.  105  AND  106.  —  CHEMICAL  CHANGES  IN  BATH  AND  SLAG  IN  A  BASIC 
OPEN-HEARTH    FURNACE. 

while  the  proportion  of  carbon  and  manganese  is  somewhat  reduced, 
as  shown  by  Figs.  105  and  106,  which  also  show  the  chemical 


148  THE  METALLURGY   OF   IRON  AND   STEEL 

changes  that  take  place  during  the  entire  operation.  These  reac- 
tions must  be  controlled  by  the  melter,  because  it  is  necessary 
that  the  carbon  shall  be  eliminated  last,  and  therefore  it  is  occa- 
sionally necessary  to  'pig  up7  the  charge,  i.e.,  add  pig  iron  in  order 
to  increase  the  amount  of  carbon.  On  the  other  hand,  in  case 
the  phosphorus  is  being  eliminated  very  fast,  the  oxidation  of  the 
carbon  may  be  hastened  by  'oreing  down/  as  it  is  called,  i.e., 
adding  ore  to  produce  the  reaction. 

Fe,O3  +  3C  =  2Fe  +  SCO. 

If  the  carbon  is  eliminated  before  the  phosphorus,  a  great  deal 
of  iron  will  be  oxidized,  because  the  phosphorus  does  not  protect 
it  as  much  as  the  carbon. 

When  the  charge  is  melted,  and  at  intervals  thereafter,  the 
melter  takes  a  spoon-ladle  full  of  metal  and  pours  it  into  an  iron 
mold.  As  soon  as  this  is  set  hard  it  is  cooled  in  water,  and  from 
the  appearance  of  its  fracture  the  melter  can  estimate  very  closely 
the  amount  of  carbon  and  phosphorus  it  contains.  In  many 
plants  it' is  customary  to  tap  heats  on  these  estimates  alone  and 
astonishing  accuracy  can  be  obtained  by  these  methods  as  to  the 
amount  of  carbon  contained  in  the  bath  of  steel.  In  all  large 
plants,  however,  the  laboratory  analysis  is  made  for  phosphorus 
and  usually  for  carbon  as  well,  and  these  determinations  may  be 
made  in  20  minutes  or  less. 

Functions  of  the  Slag.  —  The  functions  of  the  slag  are:  (1)  To 
absorb  and  retain  the  impurities  in  the  metal,  particularly  silicon, 
manganese  and  phosphorus,  and  as  much  sulphur  as  possible;  (2) 
to  lie  upon  the  top  of  the  bath  as  a  blanket  and  protect  it  from 
excessive  oxidation  by  the  furnace  gases;  and  (3)  to  oxidize  the 
impurities  of  the  bath  by  means  of  its  dissolved  iron  oxide,  which 
serves  as  a  carrier  of  oxygen  from  the  furnace  gases  to  the  impuri- 
ties in  the  metal. 

For  the  retention  of  phosphorus  and  sulphur,  the  slag  must  be 
rich  in  bases.  For  the  oxidizing  it  is  necessary  that  the  s7ag  shall 
be  fluid,  so  that  it  will  mix  easily  with  the  bath,  and  therefore  the 
content  of  lime  must  not  be  too  high.  During  the  boil,  when  the 
carbon  is  passing  off,  there  is  an  intimate  mixture  of  metal  and 
slag,  and  there  is  even  such  a  violent  agitation  of  the  bath  that  the 
metal  itself  is  frequently  uncovered  in  places  and  exposed  to  direct 
oxidation  by  the  furnace  gases. 


THE  OPEN-HEARTH   PROCESS  149 

The  removal  of  sulphur  is  a  variable  quantity  and  cannot  be 
altogether  depended  upon,  but  there  is  usually  a  large  loss  of  this 
element  during  the  operation,  in  spite  of  slight  additions  of  sulphur 
from  the  coal  through  the  gas.  This  sulphur  reduction  is  greatly 
assisted  if  the  slag  is  thinned  out  (i.e.,  its  melting-point  reduced) 
by  the  addition  of  calcium  fluoride  (CaF2)  just  before  the  end  of 
the  operation.  The  higher  the  slag  is  in  lime,  provided  it  remains 
at  the  same  time  fluid,  the  more  complete  in  general  will  be  the 
sulphur  elimination,  but  over  55  per  cent,  of  lime  usually  makes 
the  slag  viscous,  unless  the  calcium  be  added  in  the  form  of  fluoride, 
or  of  chloride  (CaCl2) .  The  latter  agent  was  added  in  many  cases 
by  the  recommendations  of  E.  H.  Saniter,  but  the  practice  was 
never  general  in  the  United  States,  and  the  use  of  calcium  fluoride 
(known  as  fluorspar)  answers  most  purposes,  unless  the  sulphur 
in  the  charge  is  excessive. 

It  is  of  very  great  importance  that  the  final  slag  in  the  open- 
hearth  operation  shall  be  a  nonoxidizing  one,  lest  the  metal  itself  be 
full  of  oxide  and  very  'wild/  i.e.,  give  off  gas  abundantly  during 
solidification.  Therefore  no  ore  should  be  added  within  two  or 
three  hours  of  the  finish  of  the  operation.  For  this  reason  there  is 
some  difficulty  in  making  steel  of  under  0.20  per  cent,  carbon  by 
the  open-hearth  process,  and  the  difficulty  increases  almost  in 
geometric  ratio  as  the  carbon  is  reduced  lower  and  lower,  be- 
cause iron  retains  with  tremendous  affinity  the  last  traces  of 
carbon,  and  it  requires  a  most  powerful  influence  to  separate  them. 
Open-hearth  managers  usually  refuse  to  take  orders  for  steel 
under  0.10  per  cent,  carbon,  except  where  consumers  own  their 
own  plant. 

Slag. — Basic  slags  will  contain : 

10  to  20  per  cent.  SiO2 
45  to  55  per  cent.  CaO 
10  to  25  per  cent.  FeO 
5  to  15  per  cent.  P2O6. 

Weight  of  Slag.  —  The  slag  made  will  depend  upon  the  silicon 
and  phosphorus  and  dirt  in  the  metal,  and  will  average  from  10  to 
30  per  cent,  of  the  weight  of  metal.  Since  the  slag  takes  practi- 
cally all  the  lime  charged  into  the  furnace,  its  weight  can  be  calcu- 
lated with  sufficient  accuracy  by  the  same  formula  given  for  calcu- 
lating the  blast-furnace  slag:  Divide  the  total  lime  (CaO)  used 


150  THE  METALLURGY  OF   IRON  AND  STEEL 

with  the  charge  (plus  30  per  cent,  of  itself  to  allow  for  wear  of  the 
lining)  by  the  percentage  of  lime  in  the  slag. 

Loss.  —  The  weight  of  steel  produced  will  be  a  variable  propor- 
tion of  the  weight  of  metal  charged,  depending  upon  the  amount  of 
pig  iron  in  the  charge,  the  amount  of  ore  used,  the  extent  to  which 
the  carbon  was  eliminated  before  tapping,  etc.,  but  it  will  average 
perhaps  93  to  96  per  cent.,  the  difference  being  made  up  as  follows, 
in  a  typical  example : 

ANALYSIS  OF  CHARGE 
(50  per  cent,  pig;  50  per  cent,  scrap) 

Pig  Iron        Scrap       Average         Loss 
per  cent,    per  cent,  per  cent,     per  cent. 

Carbon 3.75  0.25  2.00  2.00 

Silicon 0.70  0.06  0.38-  0.38 

Manganese 1.10  0.40  0.75  0.75 

Phosphorus 1.30  0.04  0.67  0.67 

Sulphur 0.37  0.03  0.20  0.20 

20  per  cent,  slag  @  12£  per 

cent.  Fe 2.50 

6.50 
Iron  reduced  from  ore 1 . 50  per  cent,  gain 

Net  loss 5 . 00 

Recarburizing.  —  Steel  must  not  be  recarburized  in  the  pres- 
ence of  a  basic  slag,  lest  the  carbon,  silicon,  and  manganese  of  the 
recarburizer  reduce  phosphorus  from  the  slag  and  cause  it  to  pass 
back  into  the  metal : 

2(3 CaO.  P2O&)  +  50=  6CaO.  P206  +  SCO  +  2P 
4(3  CaO.  P2O5)  +  5  Si  =  2(6  CaO.  P2O6)  +  5SiO2  +  4  P. 

Therefore  in  basic  practice  the  recarburizer  is  added  to  the  stream 
of  metal  while  it  is  pouring  from  the  furnace  into  the  ladle,  and 
special  arrangements  are  made  for  allowing  the  slag  which  floats 
on  top  of  the  metal  to  overflow  at  the  top  of  the  ladle  and  thus  be 
gotten  rid  of  in  a  large  part.  In  careful  practice  '  rephosphoriza- 
tion'  need  not  exceed  0.01  to  0.02  per  cent,  of  the  steel,  although  a 
much  larger  increase  may  take  place  through  accident. 

The  recarburizer  usually  consists  of  ferromanganese,  together 
with  anthracite  coal,  charcoal  or  coke  which  is  broken  into  small 
pieces  and  loaded  into  paper  bags.  About  45  per  cent,  of  the 
broken  coke  is  burned  and  the  other  55  per  cent,  will  be  dissolved 


THE   OPEN-HEARTH  PROCESS 


151 


by  the  steel.  It  is  practically  impossible  to  melt  spiegeleisen  in 
the  cupola,  because  a  cupola  must  be  run  continuously  in  order  to 
do  satisfactory  work,  while  the  open-hearth  process  is  too  slow  and 
too  irregular  to  use  a  continuous  supply  of  molten  recarburizer. 


In  making  soft  steel  the  carbon  is  reduced  to  about  0.10  or  0.15 
per  cent,  in  the  bath,  and  then  the  necessary  amount  of  recarburizer 
is  added.  In  making  high  carbon  steel,  on  the  other  hand,  two 


.90 


.80 


Diagram  Showing  Variations  in  Composition 
of  a  Normal  Acid 
Open  Hearth  Heat 


FIG.    108. 


THE  OPEN-HEARTH  PROCESS  153 

methods  are  possible:  We  may  reduce  the  bath  to  0.10  or  0.15  per 
cent,  and  then  add  sufficient  recarburizer  to  bring  the  carbon  up 
to  the  desired  point,  or  we  may  bring  the  bath  down  to  only  slightly 
below  the  desired  point  and  recarburize  it  to  the  desired  percentage. 
The  former  practice  usually  frees  the  steel  more  completely  from 
gas  and  therefore  makes  it  less  wild,  besides  reducing  the  danger 
of  phosphorus  being  left  in  the  steel. 

ACID  OPEN-HEARTH  PRACTICE 

Acid  open-hearth  practice  is  in  many  respects  similar  to  basic, 
but  the  operations  are  shorter  because:  (1)  a  much  larger  propor- 
tion of  steel  scrap  is  used;  (2)  phosphorus  is  not  removed;  and  (3), 
no  fluxes  are  added,  except  in  rare  instances,  when  a  little  silica  is 
charged  at  the  beginning  to  prevent  iron  oxide  cutting  the  lining. 

Chemistry.  —  The  chemistry  of  the  acid  process  is  much  sim- 
pler, because  neither  phosphorus  nor  sulphur  is  removed;  there- 
fore it  is  necessary  to  start  with  pig  iron  and  scrap  low  in  both  of 
these  elements.  The  progress  of  the  operation  is  shown  in  Fig. 
108.  The  manganese  in  the  pig  iron  for  acid  work  is  usually  not 
so  high  as  it  is  for  basic  work:  (1)  Because  this  element  is  some- 
times costly;  (2)  because  it  increases  the  amount  of  slag  made; 

(3)  because  it  forms  a  base  which  requires  silica  for  fluxing  it;  and 

(4)  because  it  increases  the  waste,  since  all  the  manganese  burned 
represents  a  loss  in  weight  of  metal  purchased.     Therefore  the 
manganese,  as  well  as  the  silicon  in  the  bath,  is  usually  reduced 
to  only  a  trace  by  the  time  the  charge  is  melted.     H.  H.  Campbell 
has  shown  that  the  open-hearth  slag  at  the  end  of  the  acid  opera- 
tion automatically  adjusts  itself  to  contain  about  46  per  cent,  of 
bases   (FeO  +  MnO),  the  remainder  being  principally  silica,  and 
that  this  ratio  remains  almost  the  same  even  when  very  varying 
amounts  of  iron  oxide  are  added. 

Loss.  —  The  loss  in  the  acid  process  will  not  be  as  large  as  in 
the  basic,  because  the  pig  iron  and  scrap  charged  are  not  so  im- 
pure, and  because  the  amount  of  slag  made  and  the  amount  of  iron 
oxidized  and  retained  by  the  slag  are  not  so  large.  The  loss  will 
vary  on  an  average  from  3  to  5  per  cent.,  so  that  the  final  metal 
will  weigh  95  to  97  per  cent,  of  the  weight  of  the  charge.  The 
analysis  of  this  difference  is  as  shown  on  page  154. 


154 


THE  METALLURGY  OF   IRON   AND   STEEL 


ANALYSIS  OF  CHARGE 
(50  per  cent,  pig;  50  per  cent,  scrap) 


Carbon 

Pig  Iron 
per  cent. 

3   75 

Scrap 
per  cent. 

0.25 

Average       Loss 
per  cent,   per  cent. 

2.00           2   00 

Silicon 

....       0  90 

0.10 

0.50        0  50 

Manganese 

0  .  60 

0.40 

0  .  50         0  .  50 

Phosphorus 

0  .  035 

0.045 

0  .  04         0  .  00 

Sulphur 

0.028 

0.032 

0.03        0.00 

8  per  cent,  slag  (c 
Fe.  -  .  . 

&  25  per  cent. 

.   2.00 

5.00 
Iron  reduced  from  ore  = 1 . 20  gain 


Net  loss 3.80 

Recarburiz  ng.  —  Recarburization  may  take  place  in  the  fur- 
nace in  the  acid  process,  if  desired,  because  there  is  practically  no 
phosphorus  in  the  slag  to  be  reduced  and  absorbed  by  the  metal. 
This  method  has  the  advantage  of  the  recarburizer  being  more  thor- 
oughly mixed  with  the  bath,  but  it  has  the  disadvantage  of  more 


FIG.    109. 


manganese  being  burned  out  of  the  metal  after  the  recarburizer  is 
added  and  before  the  charge  is  all  run  into  the  ladle.  The  recar- 
burizer consists  of  ferromanganese,  broken  in  pieces  not  larger 


THE  OPEN-HEARTH  PROCESS  155 

than  a  silver  dollar.  It  is  sometimes  heated  red-hot,  but  not 
always  so,  because  the  heat  of  the  metal  will  readily  melt  it.  As 
in  the  basic  practice,  recarburization  of  high  carbon  steel  may  be 
effected  either  by  burning  the  bath  down  to  a  low  point  and  then 
bringing  it  up  again  with  carbon  and  ferromanganese,  or  by  redu- 
cing it  only  slightly  below  the  desired  amount  and  then  adding 
ferromanganese  only. 

In  acid  practice,  if  the  carbon  is  burned  to  a  low  point  and  then 
brought  back,  it  is  customary  to  accomplish  this  by  dissolving  the 
requisite  amount  of  pig  iron  in  the  bath  before  adding  the  ferro- 
manganese. This  could  not  be  done  in  the  basic  furnace,  because 
the  impurities  in  the  added  pig  iron  would  be  liable  to  cause  a 
rephosphorization  of  the  metal  from  the  slag. 

Weight  of  Slag.  —  The  weight  of  slag  made  in  the  acid  process 
may  be  determined,  according  to  the  method  of  H.  H.  Campbell,1 
from  the  tota  amount  of  manganese  in  the  furnace,  which  will 
include  that  put  in  with  the  charge  (including  any  that  may  have 
been  in  the  ore)  and  that  added  with  the  recarburizing.  First  we 
subtract  from  this  total  the  amount  of  manganese  in  the  metal 
tapped;  the  weight  of  the  remainder  is  then  divided  by  the  per- 
centage of  the  manganese  in  the  slag,  which  gives  the  weight  of  the 
slag.  The  amount  of  acid  slag  will  depend  primarily  upon  the 
amount  of  silicon  in  the  charge  and  will  vary  on  the  average  from 
6  to  18  per  cent,  of  the  weight  of  the  metal  charged,  about  three- 
fourths  of  which  is  formed  during  the  melting  period.2 

Coal  Burned.  —  The  amount  of  fuel  used  per  ton  of  steel  made 
in  the  acid  open-hearth  furnace  will  be  perhaps  50  to  100  Ib.  less 
than  in  the  basic  furnace,  but  will  depend  again  upon  many  vary- 
ing conditions,  so  that  figures  should  be  used  only  with  caution. 
(See  pages  144,  167,  and  169). 

SPECIAL  OPEN-HEARTH  PROCESSES 

It  might  seem  as  if  the  use  of  molten  pig  iron  direct  from  the 
blast  furnace,  or  through  the  medium  of  a  mixer,  might  be  as 
advantageous  in  open-hearth  practice  as  in  Bessemer;  but  this  is 
not  so,  because  the  metal  in  the  open-hearth  is  subjected  to  oxida- 
tion at  the  same  time  that  it  is  being  melted,  so  that  charging 

1  See  page  275  of  No.  2.     Old  edition,  on  page  8  herein. 

2  In  the  case  of  making  structural  steel  (say  0.18  per  cent,  carbon). 


156  THE  METALLURGY  OF   IRON  AND   STEEL 

molten  material  does  not  shorten  the  operation  much.  The  time 
and  labor  cost  for  charging  is  less,  but  this  advantage  is  partly 
neutralized  by  the  scorification  and  wear  of  the  hearth  produced 
by  the  inpouring  stream  of  melted  metal.  About  one-half  the 
open-hearth  steel  of  America  is  made  from  molten  pig.  Where 
it  is  used  the  limestone  is  charged  first,  on  top  of  that  the  steel 
scrap  and  any  other  cold  metal,  and  finally  the  molten  metal  is 
poured  in.  In  this  way  the  hearth  is  protected  as  much  as  possi- 
ble from  being  cut. 

The  old  pig-and-ore  process  is  abandoned  very  largely,  because 
of  the  length  of  time  required  to  burn  off  the  impurities  unless 
they  are  diluted  by  steel.  It  is  difficult  for  a  novice  to  understand 
why  the  reactions  are  not  more  rapid  in  the  open-hearth  furnace, 
when  the  entire  purification  of  pig  iron  in  the  puddling-furnace  is 
accomplished  in  an  hour  and  a  half,  including  melting;  but  the 
difference  is  due  to  the  very  shallow  bath  in  the  puddling  opera- 
tion and  its  extensive  contact  with  the  fettling.  If  we  should 
attempt  to  purify  under  such  strong  oxidizing  conditions  in  the 
open-hearth  furnace,  the  molten  metal  would  boil  violently,  be- 
cause of  the  high  temperature,  and  for  the  same  reason  would  also 
become  so  charged  with  oxygen  as  to  be  worthless.  Even  at  the 
low  temperature  of  the  puddling-furnace,  the  boiling  is  so  violent 
as  to  increase  the  height  of  the  bath,  and  this  action  would  be  pro- 
portionately increased  at  the  temperature  of  the  open-hearth  fur- 
nace, which,  at  the  end  of  an  operation  producing  dead-soft  steel, 
will  be  about  1650°  to  1700°  C.  (3002°  to  3092°  F.) .  The  increase  in 
volume  of  the  metal  when  carbon  monoxide  gas  is  escaping  from 
it  may  be  likened  to  that  of  champagne  when  the  drawing  of  the 
cork  allows  a  rapid  escape  of  gas.  There  is  another  reason  why  the 
boil  causes  more  of  an  increase  in  the  volume  of  the  bath  in  the 
open-hearth  furnace  than  in  the  puddling-furnace:  in  the  latter, 
the  carbon  monoxide  has  only  molten  metal  and  slag  to  bubble 
through,  but  in  the  open-hearth  process,  where  cold  ore  is  added  to 
the  charge,  it  produces  a  certain  amount  of  chilling  of  the  metal 
and  slag  adjacent  to  it,  and  the  gas  having  to  bubble  through  this 
somewhat  pasty  material  causes  a  greater  increase  in  its  bulk. 
By  the  time  the  puddling  charge  becomes  pasty,  the  carbon  is 
largely  gone  and  therefore  there  is  not  a  violent  action. 

Various  attempts  have  been  made  by  different  metallurgists 
to  adapt  the  open-hearth  process  to  the  use  of  all  pig  iron  rapidly 


THE  OPEN-HEARTH  PROCESS  157 

oxidized  by  iron  ore  or  other  agencies,  and  this  has  led  to  the 
Talbot  and  the  Monell  processes,  each  of  which  is  carried  on  in  a 
single  furnace,  molten  pig  iron  being  acted  upon  by  a  highly 
oxidized  liquid  slag,  formed  prior  to  the  addition  of  the  pig  iron 
in  the  Talbot  process  and  coincident  with  it  in  the  Monell  process. 
It  has  also  led  to  the  Duplex  process,  whereby  a  large  proportion 
of  the  oxidation  is  effected  in  an  acid  Bessemer  converter,  the 
operation  being  completed  in  a  basic  open-hearth. 

Talbot  Process.  —  The  Talbot  process  has  a  basic  lining  and 
contains  a  charge  as  high  as  200  tons  in  some  cases,  as,  for  ex- 
ample, at  the  Jones  &  Laughlin  plant,  in  Pittsburg,  Pa.  As 
the  bath  of  metal  is  over  3  ft.  deep,  however,  which  is  about  twice 
that  of  an  ordinary  bath,  the  furnace  is  only  as  large  in  other 
dimensions  as  a  100-ton  furnace.  The  tilting  furnace  is  used  in 
order  that  any  desired  quantity  of  metal  or  slag  may  be  poured 
out  at  will.  The  operation  is  continuous  and  the  furnace  is  drained 
of  metal  only  once  a  week.  After  the  charge  has  been  worked 
down  to  the  desired  percentage  of  carbon,  the  great  part  of  the 
slag  is  poured  off,  and  then  about  one-third  (52  tons)  of  the  steel 
is  poured  into  the  ladle,  recarburized,  and  teemed  into  the  ingot 
molds  in  the  usual  way.  To  the  charge  of  metal  left  in  the  bath 
is  now  added  iron  ore  and  limestone  to  produce  a  basic  and  highly 
oxidized  slag,  and  through  this  slag  is  then  poured  an  amount  of 
pig  iron  equal  to  the  steel  removed.  The  reaction  between  the 
impurities  in  the  pig  iron  and  the  iron  oxide  in  the  slag  is  very 
vigorous,  but  does  not  cause  a  frothing  or  foaming,  because  all  the 
materials  are  in  the  liquid  form  and  the  gas  bubbles  through  them 
without  great  difficulty. 

The  oxidation  is  so  rapid  that  the  silicon  and  manganese  are 
said  to  be  oxidized  almost  immediately,  and  then  the  phosphorus 
and  carbon  are  worked  off  in  the  usual  way,  using  more  ore  and 
limestone,  if  necessary.  The  temperature  is  low  at  first,  in  order 
that  the  phosphorus  may  be  more  readily  burned.  At  the  end  of 
about  four  to  six  hours,  the  bath  has  again  become  purified,  and 
50  tons  of  metal  are  removed,  the  whole  operation  being  then  re- 
peated. The  yield  of  steel  is  106  to  108  per  cent,  of  the  weight  of 
the  pig  iron  charged,  because  of  the  large  amount  of  iron  reduced 
from  the  ore  by  the  impurities  in  the  pig  iron. 

3  C  +  FeaO3  =  2  Fe  +  3  CO  (absorbs  108,120  calories). 


158  THE   METALLURGY   OF   IRON   AND   STEEL 

The  advantages  of  the  process  are:  We  obtain  three  or  four 
heats  of  50  tons  each  in  24  hours  without  the  use  of  steel  scrap ;  the 
yield  is  large  (though  this  advantage  is  somewhat  neutralized  by 
the  cost  of  the  iron  ore  used);  and  the  temperature  of  the  final 
metal  can  be  more  easily  controlled.  The  disadvantages  of  the 
process  are :  The  very  large  cost  of  furnaces  1  and  the  slightly 
higher  cost  for  repairs. 

Monell  Process.  —  Mr.  A.  Monell,  when  metallurgist  of  the 
Carnegie  Steel  Company,  developed  a  pig-and-ore  process  in  which 
highly  heated  oxidizing  and  slag-making  materials  were  made  to 
react  with  the  impurities  in  molten  pig  iron  without  the  necessity 
of  having  a  reservoir  of  metal  into  which  to  pour  it.  Upon  a 
basic  hearth  he  heats  limestone  and  a  relatively  large  amount 
of  ore  until  they  begin  to  melt,  and  then  pours  molten  pig  iron, 
equivalent  to  the  capacity  of  the  furnace,  upon  it.  The  tem- 
perature of  the  bath  is  necessarily  low,  since  pig  iron  direct  from 
a  blast  furnace  or  from  a  mixer  will  not  be  more  than  200°  or 
300°  C.  above  its  melting-point,  and  therefore  the  phosphorus 
will  be  oxidized  very  rapidly.  The  slag  foams  up  and  pours 
out  of  a  slag-notch  that  is  provided  for  the  purpose,  and  in  an  hour 
the  bath  is  practically  free  from  phosphorus,  silicon,  and  man- 
ganese, and  most  of  the  slag  is  removed.  The  operation  is  then 
continued  in  the  usual  way  to  eliminate  the  carbon,  and  the 
metal  is  tapped  when  this  has  been  reduced  to  the  desired  point. 
The  American  rights  to  the  process  are  owned  by  the  Carnegie 
Steel  Company  and  they  are  operating  it  at  many  of  their  fur- 
naces. No  details  are  known  generally,  but  it  is  to  be  presumed 
that  the  results  are  favorable.  The  apparent  disadvantages  of 
the  process  are  excessive  cutting  of  the  hearth  and  a  heavy  loss 
of  iron  in  the  rich  slag  which  flows  off  at  the  beginning  of  the  opera- 
tion. The  Monell  process  has  been  used  successfully  in  England, 
with  pig  iron  containing  up  to  2  per  cent,  of  phosphorus. 

Duplex  Process.  —  At  Witkowitz,  Austria,  at  Ensley,  Alabama, 
at  Monterey,  Mexico,  at  Sidney,  Nova  Scotia,  and  at  Pueblo, 
Colorado,  the  combined  Bessemer  and  basic  open-hearth  process 
is  in  operation,  an  acid  converter  being  used  to  oxidize  the  silicon, 
manganese,  and  most  of  the  carbon,  while  the  phosphorus  and  the 

1  It  is  stated  that  the  first  200-ton  furnace  at  the  Jones  &  Laughlin  works 
cost  $1,000,000  to  build;  but  with  the  present  experience  they  can  be  installed 
for  about  one-fourth  of  that  sum. 


THE  OPEN-HEARTH  PROCESS  159 

remainder  of  the  carbon  is  eliminated  in  a  basic  open-hearth  fur- 
nace. In  the  different  localities  there  are  different  ways  of  carry- 
ing out  this  combination,  but  these  divide  themselves  into  two 
general  methods:  In  one  method,  the  metal  is  blown  in  the  con- 
verter until  it  is  purified  to  the  point  where  it  is  practically  equiva- 
lent to  so  much  high-phosphorus,  molten  steel  scrap,  which  is  then 
mixed  with  either  liquid  or  solid  pig  iron  in  the  open-hearth  furnace 
and  worked  as  any  ordinary  pig-and-scrap  heat  after  melting.  In 
another,  and  more  common,  method,  the  pig  iron  is  blown  in  the 
converter  until  it  contains  about  1  per  cent,  or  so  of  carbon,  and 
this  product,  with  little  or  no  additional  pig  iron,  is  then  dephos- 
phorized and  completely  decarbonized  in  the  open-hearth  furnace. 
It  is  stated  that  the  total  time  of  the  purification  is  less  than  if  the 
ordinary  basic  open-hearth  process  were  used  (this  is  4  to  7  hours 
in  Alabama,  while  the  open-hearth  part  of  the  process  is  about  3 
hours  at  Witkowitz),  and  that  the  total  loss  isjonjy  10  per  cent. 

At  Alabama,  the  metal  from  two  20-ton  converters  is  poured 
into  a  mixer  furnace  of  250  tons  capacity,  which  supplies  four  100- 
ton  basic  open-hearth  furnaces  writh  metal.  The  blown  metal  con- 
tains about  1  per  cent,  of  carbon,  about  one-half  the  heats  being 
blown  'full/  while  the  remainder  are  blown  to  about  1.75  to  2.50 
per  cent,  carbon.  In  this  connection  it  is  interesting  to  note  that, 
if  the  metal  is  blown  to  about  1.75  per  cent,  or  so  of  carbon,  there  is 
less  loss  of  iron  as  shots  in  the  slag  than  if  the  carbon  is  higher.1 

Processes  in  Two  Open-Hearth  Furnaces.  —  At  a  low  tempera- 
ture, phosphorus  is  very  easily  oxidized  and  absorbed  by  a  basic 
slag,  even  in  the  presence  of  carbon,  but  when  the  heat  is  high  the 
oxidation  of  phosphorus  is  hindered  by  the  carbon,  for  the  reason 
already  explained,  —  that  the  affinity  of  carbon  for  oxygen  in- 
creases more  rapidly  with  the  temperature  than  the  affinity  of  the 
other  elements  in  the  bath.  This  explains  the  rapid  elimination 
of  phosphorus  in  the  puddling  process,  where  the  slag  is  strongly 
basic  with  oxide  of  iron  and  the  temperature  is  low.  We  could 
obtain  the  same  conditions  in  the  beginning  of  the  open-hearth 
process,  but  the  operation  would  be  extremely  slow  at  this  low 
heat,  and  the  carbon  would  pass  away  slowly.  These  difficulties 
have  been  met  by  the  Campbell  No.  2  and  Bertrand-Thiel  proc- 
esses, the  former  of  which  was  developed  at  Steelton,  Pa.,  and  the 
latter  at  Kladno,  Bohemia. 

1  For  this  information  I  am  indebted  to  Mr.  Hugh  P.  Tiemann. 


160      THE  METALLURGY  OF  IRON  AND  STEEL 

Campbell  No.  1  Process.  —  The  pig-and-ore  process  using 
molten  metal  has  long  been  in  operation  in  the  Campbell  tilting 
furnace,  and  the  frothing  of  the  bath  is  taken  care  of  by  tipping  the 
furnace  backward  so  that  no  slag  or  metal  will  pour  out  of  the  door, 
though  a  large  amount  of  the  former  flows  from  the  slag-hole  be- 
tween the  ends  of  the  furnace  and  the  ports.  The  operation  is 
continued  in  this  way  for  two  or  three  hours,  since,  as  already 
noted,  the  furnace  can  be  tipped  without  cutting  off  the  supply  of 
gas  and  air,  and  the  yield  of  steel  is  104  to  106  per  cent,  of  the  pig 
iron  charged. 

Campbell  No.  2  Process. — At  the  same  plant  there  is  also  a 
combination  process  in  which  the  charge,  consisting  of  all  pig  iron, 
or  of  pig  iron1  and  scrap,  is  placed  in  a  basic  open-hearth  furnace, 
and  the  purification  carried  on  at  a  high  temperature  until  almost 
all  the  silicon  and  phosphorus  and  part  of  the  sulphur  and  carbon 
are  eliminated.  The  bath  is  then  tapped  from  the  basic  furnace 
and  poured  into  an  acid-lined  furnace,  care  being  taken  that  none 
of  the  basic  slag  goes  with  it.  At  this  period  the  metal  is  low  in 
phosphorus  and  sulphur,  and  contains  about  the  same  amount  of 
carbon  that  a  cold  charge  would  have  contained  as  soon  as  melted. 
The  conditions  are  therefore  the  same  as  if  low-phosphorus  low- 
sulphur  material  had  been  charged  into  an  acid  furnace  and 
melted  there,  and  the  process  is  now  continued  at  a  higher  tem- 
perature, in  the  usual  way  to  make  acid  open-hearth  steel.  The 
disadvantage  of  this  process  is  that  the  transferring  of  molten 
metal  from  one  furnace  to  another  is  not  an  easy  matter,  nor, 
in  fact,  is  it  possible  with  the  arrangements  in  many  plants. 

OPEN-HEARTH  FUELS 

The  commonest  fuel  used  in  the  open-hearth  furnace  is  pro- 
ducer gas,  because  more  heating  power  and  more  gas  can  be  ob- 
tained for  a  dollar  in  this  variety  than  in  any  other,  except  in 
those  favored  localities  where  natural  gas  is  found. 

Producer  Gas.  —  If  air  be  blown  through  red-hot  carbon  the 
following  reaction  takes  place: 

C  +  20  =  C02; 

but  if  the  bed  of  fuel  is  deep,  the  carbon  dioxide  enters  into  a 
further  reaction,  as  follows : 

CO2  +  C  =  2  CO. 
1  The  pig  iron  charged  may  be  either  in  the  liquid  or  solid  state. 


THE  OPEN-HEARTH  PROCESS 


161 


In  other  words,  if  air  be  made  to  blow  through  a  deep  bed  of  red- 
hot  carbon,  there  will  be  produced  carbon  monoxide  gas  which  has 
combustible  value: 

CO  +  O  =  CO2  (generates  68,040  calories). 

Producer  gas  for  open-hearth  furnaces  is  usually  made  from 
bituminous  coal,  because  the  hydrocarbons  contained  in  this  coal 
enter  into  the  gas  and  thus  give  it  illuminating  power,  which 
makes  it  much  more  efficient  in 
the  furnace,  because  the  heating 
takes  place  by  radiation  chiefly. 
Such  a  gas  will  contain  3  to  5 
per  cent,  of  hydrocarbons,  20  to 
25  per  cent,  of  CO,  55  to  60  per 
cent,  of  nitrogen,  and  2  to  8  per 
cent,  of  carbon  dioxide. 

The  two  latter  components 
produce  no  heat  and  are  there- 
fore worse  than  useless,  because 
they  carry  heat  away  from  the 
furnace  up  the  chimney  stack. 
The  nitrogen  comes  from  the  air, 
of  course,  but  the  CC>2  is  theoreti- 
cally absent.  Its  presence  is  due 
to  irregularities  in  the  gas  pro- 
ducer operation,  such  as  vertical 
channels  forming  in  the  bed  of 
fuel,  up  which  the  CO2  gas  passes 
without  being  brought  into  con- 
tact with  carbon;  or  the  rapid 
passage  of  the  gas  does  not  per- 
mit time  for  the  reactions  to  be 
completed;  or  irregularities  in  the  fuel  bed,  whereby  the  fuel  will 
be  red-hot  much  higher  on  one  side  than  on  the  other. 

The  air  is  usually  blown  through  the  fuel  by  means  of  a  steam- 
jet,  which  results  in  a  certain  amount  of  steam  passing  into  the 
producer  with  the  air;  but  this  is  rather  an  advantage  than  other- 
wise, as  the  steam  is  decomposed  by  the  red-hot  carbon  and  en- 
riches the  producer  gas : 

H2O  +  C  =  2H  +  CO; 
(2H  +  O  =  H2O:  generates  58,060  calories). 


FIG.    110.— TAYLOR  REVOLVING 
BOTTOM   GAS    PRODUCER. 


162  THE  METALLURGY  OF   IRON   AND   STEEL 

Gas  Producers.  —  The  gas  producers  are  the  furnaces  in  which 
the  fuel  is  contained  while  the  air  is  passed  through  it.  The  main 
objects  to  be  accomplished  are:  (1)  To  pass  the  air  uniformly 
through  the  bed;  (2)  to  remove  ashes  and  charge  fresh  fuel  with- 
out interrupting  the  production  of  gas;  and  (3)  to  preserve  the 
deep  bed  of  incandescent  carbon,  having  level  upper  and  lower 
surfaces.  There  are  three  horizontal  zones  in  the  gas  producer: 
The  first  is  the  ash  zone,  which  is  deep  in  order  that  the  air  may  be 
slightly  preheated  in  passing  through  it  and  that  any  unburned 
carbon  which  gets  into  it  may  have  a  strong  liability  of  being 
burned.  Next  above  that  is  the  C(>2  zone,  in  which  the  oxygen 
and  carbons  are  first  combined;  and  above  that  the  CO  zone,  in 
which  the  CO2  is  reduced  by  more  carbon.  The  top  of  this  zone 
should  be  at  a  dull-red  heat. 

There  are  many  different  forms  of  producer,  which  are  exten- 
sively used  for  open-hearth  work,  but  these  may  be  divided  into 
two  general  types :  In-  the  first  or  water-sealed  type,  the  bottom 
of  the  producer  dips  into  a  pool  of  water  and  thus  the  tools  may 
be  introduced  for  the  removal  of  the  ashes  at  will.  In  this  type 
there  are  sometimes  steel  arms  extending  into  the  bed  of  fuel, 
either  from  the  top  or  from  a  central  shaft,  by  the  rotation  of  which 
the  bed  is  polled,,  lumps  and  channels  are  broken  up,  etc.  The 
second  type  has; a  mechanical  grate,  by  which  the  ashes  can  be 
scraped  down  into  the  chamber  underneath  without  interrupting 
the  producer  operation  for  the  purpose. 

Grate  Area.  —  The  total  grate  area  of  all  the  producers  supply- 
ing gas  to  a  furnace  should  be  about  3.5  sq.  ft.  per  ton  of  furnace 
capacity;  some  producer  plants  run  even  higher  than  this,  and  up 
to  6.25  sq.  ft.  Another  method  of  figuring  the  grate  area  is  that 
1  sq.  ft.  should  be  supplied  for  every  7.5  to  12.5  Ib.  of  coal  burned 
per  hour,  although  with  expert  gas  makers  and  good  coal  the  com- 
bustion may  be  much  greater  than  this,  and  higher  values  (to  22 
Ib.)  are  claimed  by  the  makers  of  the  gas  producers. 

Volume  and  Calorific  Power.  —  The  volume  of  producer  gas 
obtained  from  a  ton  of  coal  will  be  about  150,000  to  170,000  cu.  ft., 
having  a  calorific  power  of  33  to  36  Calories  per  cu.  ft.,  or  130  to 
145  B.t.u.  per  cu.  ft.1  These  figures  will,  of  course,  depend 
upon  the  quality  of  the  coal  gasified,  but  the  calorific  power  is  no 

1  For  calculation  of  this  relation  see  page  171. 


FIG.    111. —  MORGAN   WATER-SEALED   GAS   PRODUCER. 


164 


THE   METALLURGY   OF   IRON   AND   STEEL 


more  important  than  the  amount  of  heat  that  it  will  radiate,  which 
depends  upon  the  luminosity  of  the  flame. 

Luminosity.  —  The  luminosity  of  flames  depends  upon  the 
amount  of  hydrocarbons,  and  especially  of  heavy  hydrocarbons, 


FIG.    112.  —  HUGHES   MECHANICALLY   POKED    GAS    PRODUCER. 

burned  to  produce  them.  It  is  therefore  necessary,  if  the  pro- 
ducer gas  is  made  from  bituminous  coal  low  in  hydrocarbons  or 
from  coke  or  anthracite,  to  increase  its  illuminating  power  by 


THE  OPEN-HEARTH  PROCESS  165 

spraying  oil  into  it.  The  luminosity  is  produced  by  the  deposition 
of  a  myriad  of  tiny  particles  of  carbon,  which  are  heated  to  incan- 
descence and  then  radiate  energy  in  the  form  of  light.  It  is  prob- 
able that  this  action  is  produced  by  the  relatively  light  hydrocar- 
bons, such  as  methane  (CH4),  breaking  up  first  into  ethylene 
(C2H4) ,  and  then  into  acetylene  (C2H2) ,  which  deposits  the  carbon 
particles  or  soot.  It  is  for  this  reason  that  the  pure  acetylene 
flame  has  such  intense  luminosity. 


FIG    113.  — BUTTERFLY   REVERSING   VALVE. 
(See  also  Fig.  32,  page  56.) 

Gas  Mains.  —  The  gas  mains  leading  from  the  producer  plant 
to  the  open-hearth  furnace  should  be  lined  with  brick  and  be  at 
least  large  enough  for  a  man  to  pass  through.  Beyond  this,  a 
good  rule  is  1  sq.  ft.  of  area  of  cross-section  of  gas  main  for  every 
8  sq.  ft.  of  total  combined  area  of  gas-producer  grates.  The  gas 
loses  heat  by  radiation  in  the  mains  and  deposits  the  tarry  constit- 
uents, i.e.,  the  nearly  solid  hydrocarbons,  in  both  ways  losing 
heating  power. 


166 


THE  METALLURGY  OF   IRON   AND   STEEL 


Valves.  —  The  reversing  valves  of  the  open-hearth  furnace  are  a 
cause  of  large  loss  in  producer  gas,  and  sometimes  the  leak  amounts 
to  10  or  20  per  cent.  Ordinary  leaks  may  be  prevented  by  having 
water-sealed  valves,  but  sometimes  the  pressure  of  gas  reaches  the 
point  where  it  overcomes  the  water  pressure  and  escapes,  causing 
a  heavy  loss.  Moreover,  water-sealed  valves  are  open  to  serious 
objections:  (1)  The  water  may  freeze,  causing  an  endless  amount 
of  annoyance  and  trouble;  (2)  some  water  on  the  inside  of  the 
valve  is  vaporized  and  the  vapor  carried  into  the  regenerator  or 
into  the  furnace,  where  it  absorbs  heat;  (3)  the  hoods  are  liable  to 
warp  with  the  heat;  and  (4)  valves  of  this  type  are  so  heavy  that 
elaborate  mechanism  is  necessary  to  reverse  them.  The  common 
butterfly  valves  burn  out  rapidly  and  warp  badly.  If  water- 


FIG.    114. 

sealed,  the  hoods  warp  and  leak.  Lining  the  hoods  with  brick 
makes  additional  weight  for  shifting  and  adds  very  largely  to  the 
repairs.  The  mushroom  type  requires  eight  valves  to  a  furnace 
and  an  elaborate  arrangement  for  reversing  them  properly.  They 
burn  out  badly  unless  water-cooled,  when  difficulty  is  met  with 
from  freezing. 

Natural  Gas.  —  In  those  districts,  like  Pittsburg,  where  natural 
gas  occurs,  it  is  a  great  boon  to  the  open-hearth  steel  industry, 
because  of  its  high  calorific  power  and  the  cheapness  with  which  it 
may  be  obtained,  and  about  80  wrought-iron  plants  and  90  steel 
plants  in  America  use  it.  It  is  drawn  from  the  earth,  and  has  a 
calorific  power  of  970  to  1010  B.t.u.  per  cu.  ft.  (equivalent  to  225 
to  250  Calories  per  cu.  ft.  or  8600  to  9000  Calories  per  cu.  meter).1 

1  The  calculation  of  this  relation  will  be  found  on  page  171. 


THE  OPEN-HEARTH  PROCESS 


167 


In  the  Pittsburg  district  the  amount  of  natural  gas  used  per  ton 
of  steel  made  ranges  from  4000  to  11,000  cu.  ft.,  averaging  about 


FIG.   115.  — MUSHROOM   REVERSING  VALVE. 


~  -Furnace  Flue  '     Chimney  Flue 

FIG.    116. —WATER-SEALED   REVERSING  VALVE. 

5500.     This  includes  the  gas  used  in  the  furnace  and  the  small 
amount  necessary  for  heating  the  ladles.     The  natural  gas  is  usu- 


168 


THE  METALLURGY  OF   IRON  AND   STEEL 


ally  introduced  through  two  pipes  at  each  end  of  the  furnace, 
which  are  located  close  to  the  bottom  of  the  gas-ports  and  deliver 
the  fuel  about  3J  feet  back  from  the  hearth.  The  natural  gas  is 
therefore  applied  without  any  loss  in  gas  mains,  reversing  valves, 
regenerators,  etc.,  and  is  cheaper  in  labor  on  the  furnace  floor 
itself.  The  Pittsburg  natural  gas  averages  about  70  to  90  per 
cent,  of  methane  (CH4)  or  marsh  gas,  the  remainder  being  hydro- 
gen with  a  fraction  of  a  per  cent,  of  carbon  dioxide  and  a  very  few 
per  cent,  of  nitrogen. 

On  account  of  its  high  calorific  power,  it  is  not  necessary  to  pre- 
heat this  gas,  and  this  is  the  more  fortunate,  because  the  amount  of 


Detail  of  Washer 


Rubber  Hoee    / 


Connects-Here 

•plG.    117.  — OIL   BLOW-PIPE   FOR   OPEN-HEARTH   FURNACE. 

hydrocarbon  is  so  great  that  if  the  gas  be  passed  through  regenera- 
tive chambers,  it  decomposes  and  deposits  soot  on  the  checker- 
work.  All  the  open-hearth  furnaces  in  the  Pittsburg  district  are 
so  arranged  that  they  can  be  put  on  producer  gas  in  case  it  should 
become  necessary,  because  the  supply  of  natural  gas  has  been  de- 
creasing for  many  years.  In  the  early  part  of  1908,  some  furnace 
plants  of  a  very  important  company  in  this  district  began  the  use 
of  the  manufactured  gas,  because  of  the  increased  cost  of  natural 
gas. 

Oil.  —  On  the  continent  of  Europe,  and  in  parts  of  the  United 
States  distant  from  the  natural  gas  and  bituminous  coal  regions, 
many  open-hearth  furnaces  are  heated  by  petroleum.  The 


THE  OPEN-HEARTH  PROCESS 


169 


United  States  has  many  deposits  of  fuel  oil,  besides  which  it  is 
sometimes  possible  to  obtain  a  refuse  from  the  oil  refineries  which 
is  excellent  for  this  purpose.  There  are  therefore  many  different 
grades  employed,  but  they  will  usually  average  from  7.8  to  8.3  Ib. 
per  gallon,  with  a  calorific  power  of  14,000  to  17,000  B.t.u.  per 
pound.  H.  H.  Campbell l  states  that  a  rough  comparison  may  be 
made  by  assuming  that  50  gallons  of  oil  will  give  the  same  amount 
of  heat  as  about  1000  pounds  of  soft  coal,  and  he  has  had  a  valu- 
able amount  of  experience  with  this  kind  of  fuel.  It  would  seem, 
however,  as  if  this  value  for  oil  was  somewhat  high  for  safety  in 


Foreplate-  Level 


Charging  Floor 


FIG.    118.  — FURNACE   ARRANGED   TO   USE  OIL  BLOW-PIPE. 

making  calculations,  and  that  a  more  conservative  estimate  would 
be  to  say  that  from  35  to  60  gal.  of  oil  would  be  required  per  ton  of 
steel  treated  in  the  open-hearth  furnace.  Eight  furnaces  using  oil 
averaged  38  to  42  gal.  per  ton  of  steel  made. 

The  crude  petroleum  is  vaporized  by  atomizing  it  with  a  jet  of 
steam  or  compressed  air,  and  it  is  not  common  practice  in  the 
United  States  to  pass  this  vapor  through  a  regenerative  chamber. 
The  usual  method  of  application  is  by  a  blow-pipe  introduced 
through  the  brickwork  at  the  end"  of  the  furnace,  as  shown  in 
Fig.  118,  and  a  special  form  of  blow-pipe  is  now  on  the  market  for 
this  purpose.  It  is  necessary  to  pump  the  oil  to  the  blow-pipe  or 

1  See  page  247  of  No.  2.     Old  edition,  on  page  8  herein. 


170  THE  METALLURGY  OF   IRON  AND  STEEL 

else  to  store  it  in  an  overhead  tank,  from  which  gravity  will  carry 
it,  but  the  labor  in  connection  with  this  is  much  less  than  the  labor 
on  gas  producers.  In  the  rare  cases  when  the  oil  vapor  is  pre- 
heated, it  must  be  introduced  into  the  hot  part  of  the  regenerative 
chamber,  because  if  it  cools  it  condenses.  Moreover,  when  intro- 
duced into  a  cold  furnace  or  with  a  cold  charge  in  the  furnace, 
combustion  will  be  retarded. 

Whether  oil  is  used  or  not  will  depend  principally  upon  freight, 
because  it  may  be  transported  much  more  cheaply  than  any  other 
form  of  fuel.  It  gives  a  longer  flame  than  either  natural  or  pro- 
ducer gas,  and  one  very  great  advantage  of  using  it  is  a  saving  of 
the  roof  of  the  furnace;  the  oil  flame  may  be  directed  so  accurately 
by  means  of  the  blow-pipe  that  it  does  not  impinge  directly  on  the 
roof,  and  the  brickwork  therefore  lasts  very  much  longer.  On  the 
other  hand,  it  spreads  out  horizontally  and  causes  a  greater  wear 
on  the  front  and  back  walls  of  the  furnace.  It  gives  a  more  uni- 
form heat,  a  more  oxidizing  flame,  and  no  danger  of  losses  or  dif- 
ficulties, in  case  there  is  a  leak  in  the  walls  between  the  gas  and 
air  regenerators,  which  is  not  an  infrequent  occurrence  with  gas. 

Water-Gas.  —  If  steam  be  made  to  pass  through  a  bed  of  red- 
hot  carbon,  the  product  is  a  gas  containing  slightly  less  than  50 
per  cent,  each  of  hydrogen  and  carbon  monoxide  and  having  a 
high  calorific  power: 

C  +  H2O  =  CO  +  H2  (absorbs  28,900  calories). 

The  result  of  this  reaction  is  a  reduction  of  the  temperature  of 
the  fuel  bed,  which  is  rapidly  reduced  until  another  reaction  begins 
to  take  place: 

C  +  2H2O  =  CQs  +  4H  (absorbs  18,920  calories). 

Therefore  some  means  must  be  employed  to  raise  the  tempera- 
ture at  intervals,  and  this  is  ordinarily  accomplished  by  inter- 
rupting the  passage  of  steam  and  passing  air  through  the  fuel  bed, 
which  raises  the  temperature  and  at  the  same  time  forms  producer 
gas  which  is  used  for  other  purposes.  Usually,  it  is  necessary  to 
blow  air  through  for  12  to  15  minutes,  and  then  steam  for  4  or 
5  minutes.  Consequently,  the  manufacture  of  water-gas  is 
intermittent  and  the  method  is  not  very  satisfactory  for  open- 
hearth  work,  although  the  gas  is  used  to  some  extent  on  account 
of  its  high  calorific  power.  This  operation  produces  roughly 
;35,000  cu.  ft.  of  water-gas  and  80,000  cu.  ft.  of  producer  gas  per 


THE  OPEN-HEARTH  PROCESS 


171 


ton  of  coal.     Water-gas  has  about  2600  Cals.  per  cu.  meter,  or, 
say,  290  to  300  B.t.u.  per  cubic  foot.1 

Dellwik-Fleischer  System.  —  The  Dellwik-Fleischer  system  is 
a  modification  of  the  ordinary  water-gas  system,  in  that  the  amount 
of  air  blown  through  for  heating  up  the  fuel  is  so  very  large  that 
carbon  dioxide  is  produced  instead  of  carbon  monoxide.  This 


Air 


FIG.    119.  — WATER-GAS   PRODUCER. 


gas  is  therefore  altogether  wasted,  but  the  formation  of  carbon 
dioxide  generates  so  much  more  heat  that  the  blowing  up  does 
not  take  so  long,  and  usually  lasts  from  1£  to  2  minutes,  after 
which  water-gas  is  made  for  8  to  12  minutes.  In  this  way  about 

1  One  cubic  meter  =  35.3  cubic  feet. 
One  Calorie  =  3 .968  B.  t.  u.     (See  page  466.) 
One  Calorie  per  cubic  meter  =  8 . 9  B.  t.  u.  per  cubic  foot. 


172  THE  METALLURGY  OF  IRON  AND  STEEL 

80  per  cent,  of  the  calorific  value  of  the  fuel  is  converted  into 
water-gas,  and  several  steel-works  in  Europe  have  adopted  the 
method. 

Mond  Gas.  —  In  the  Mond  process  a  mixture  of  water-gas  and 
producer  gas  is  made  continuously.  For  every  ton  of  fuel  burned 
there  is  forced  into  the  producer  about  3  tons  of  air  and  2.5  tons 
of  steam,  the  latter  being  produced  by  absorbing  the  sensible  heat 
of  the  gas  in  the  boiler.  It  gives  about  150,000  cu.  ft.  of  gas  per 
ton  of  fuel  burned,  containing  about  25  per  cent,  of  hydrogen, 
12£  per  cent,  of  CO,  45  to  50  per  cent,  of  nitrogen,  and  12£  per  cent, 
of  CO,.  This  gives  a  slightly  higher  calorific  power  than  ordinary 
producer  gas,  and  is  used  in  some  steel-works. 


REFERENCES  ON  THE  OPEN-HEARTH  PROCESS 

61.  M.  A.  Pavlov.     "Album  of  Drawings  Relating  to  the  Manu- 

facture   of    Open-Hearth    Steel."     St.    Petersburg,    1908. 
(See  also  page  93.) 

62.  W.  M.  Carr.     "Open-Hearth  Steel   Castings."     1907.     This 

contains  a  concise,  simple  and  readily  intelligible  discussion 
of  the  acid  and  basic  open-hearth  processes  and  practice. 


VII 
DEFECTS   IN   INGOTS   AND   OTHER   CASTINGS 

BESIDES  the  dangers  already  mentioned  in  connection  with 
improper  methods  of  manufacture,  excessive  amounts  of  impuri- 
ties, etc.,  iron  or  steel  may  suffer  from  damage  caused  or  developed 
during  casting.  The  commonest  defects  which  may  appear  at  this 
time  are:  (1)  Blow-holes,  or  gas  bubbles  enclosed  in  the  body  of 
the  metal;  (2)  a  pipe,  or  shrinkage  cavity;  (3)  ingotism,  or  the 
formation  of  large-sized  crystals;  (4)  segregation,  or  the  concentra- 
tion of  impurities  in  localities;  (5)  checking  or  cracking  of  the  cast- 
ing because  of  strains  produced  when  the  metal  is  hot  and  tender. 
Avoiding  these  defects  cannot  make  bad  steel  good,  but  their  pres- 
ence may  make  good  steel  bad,  and  therefore  to  guard  against 
them  is  an  important  part  of  the  processes. 

Blow-holes.  —  Blow-holes  are  especially  liable  to  occur  in  steel, 
particularly  in  low-carbon  steel.  When  the  metal  is  in  a  molten 
state,  it  readily  dissolves  certain  gases,  such  as  hydrogen,  nitrogen, 
oxygen.  Upon  solidification  these  gases  come  out  of  their  state 
of  solution,  but  may  become  entangled  in  the  steel  and  cause  a  gas 
bubble  or  cavity  varying  all  the  way  in  size  from  microscopic 
proportions  up  to  an  inch  or  more  in  length.  The  formation  of 
these  blow-holes  is  precisely  similar  to  the  formation  of  air  bubbles 
in  ice:  water  dissolves  a  good  deal  of  air  while  in  the  liquid  state 
and,  as  we  all  know,  it  is  well-nigh  impossible  to  freeze  the  water 
without  obtaining  a  great  many  air  bubbles  in  the  ice,  due  to  the 
separation  of  this  air  during  freezing.  The  danger  in  the  case  of 
steel  is  not  so  great  as  in  the  case  of  ice,  and  it  is  by  no  means  im- 
possible to  obtain  steel  absolutely  free  from  this  defect.  Appar- 
ently, the  reason  for  this  difference  is  that  the  gas  separates  from 
steel  a  short  time  before  solidification  is  complete,  and  thus  the 
bubbles  have  some  opportunity  to  escape  before  they  are  enclosed 
in  the  solid.  Also,  steel  passes  through  a  pasty  stage  during  solid- 
ification, as  we  shall  learn  later,  and  therefore  gives  a  better 
opportunity  for  the  gas  bubbles  to  pass  away. 

173 


174  THE  METALLURGY  OF   IRON   AND   STEEL 

Another  cause  of  blow-holes  in  steel  is  undoubtedly  the  presence 
of  oxide  of  iron  in  the  metal.  This  oxide  of  iron  reacts  with  the 
carbon  added  in  the  recarburizer  and  forms  carbon  monoxide  gas 
(CO),  which  may  be  produced  during  the  entire  solidification  pe- 
riod and  thus  cause  many  blow-holes. 

Prevention  of  Blow-holes.  —  That  oxide  of  iron  is  one  of  the 
chief  causes  of  blow-holes  is  shown  by  many  things;  for  instance, 

(1)  steel  known  to  be  highly  oxidized  is  very  liable  to  blow-holes; 

(2)  cast  iron,  which  from  its  chemical  composition  can  never  be 
much  oxidized,1  is  never  subject  to  blow-holes;  and  (3)  the  addi- 
tion to  steel  of  deoxidizers  prevents  the  formation  of  blow-holes. 

Chief  among  the  deoxidizing  elements  which  are  added  for  this 
purpose  are  manganese,  silicon,  and  aluminum.  These  elements 
seem  to  act  partly  by  deoxidizing  the  iron  and  carbon,  in  both 
ways  preventing  the  formation  of  carbon  monoxide,  and  partly  by 
increasing  the  solvent  power  of  the  solid  metal  for  gases,  so  that  a 
less  amount  separates.  The  amount  of  these  deoxidizing  sub- 
stances necessary  to  be  added  will  depend  largely  upon  the  extent 
to  which  we  desire  to  prevent  the  formation  of  blow-holes.  In  the 
case  of  steel  castings  it  is  often  necessary  that  blow-holes  be  en- 
tirely prevented,  but  in  the  case  of  ingots  which  are  to  be  subse- 
quently forged  or  rolled  it  is  not  necessary  that  blow-holes  should 
be  absent  altogether,  because  they  will  be  closed  up  under  the 
pressure  of  the  mechanical  wrork  and  their  sides  welded  together. 
Indeed,  their  presence  is  sometimes  desired,  because  when  they 
separate  from  the  steel  they  occupy  space,  thereby  counteracting 
to  a  certain  extent  the  shrinkage  of  the  metal  during  solidification 
and  tending  to  reduce  the  volume  of  the  shrinkage  cavity  or  pipe. 
For  this  reason  a  small  number  in  some  harmless  locality  is  often 
intentionally  allowed  to  form  in  steel  ingots.  Mr.  Brinell  found  in 
his  steel- works  that  if  the  percentage  of  manganese  plus  5.2  times 
the  percentage  of  silicon  is  equal  to  2.05  or  more,  the  steel  will 
be  entirely  free  from  blow-holes.  In  this  case,  however,  the  pipe 
will  be  large.  If  this  sum  is  equal  to  1.66,  the  steel  will  contain  a 
harmless  number  of  minute  blow-holes,  but  the  pipe  will  be  small. 

JThat  cast  iron  is  sometimes  partially  oxidized  is  claimed  by  several 
eminent  authorities,  and  the  evidence  presented  makes  us  hesitate  to  deny  that 
a  certain  variety  of  wild  cast  iron  owes  its  peculiar  behavior  to  the  presence 
of  some  partially  oxidized  constituent  (perhaps  the  oxysulphide  of  iron,  as 
suggested  by  J.  E.  Johnson,  Jr.). 


DEFECTS   IN   INGOTS  AND  OTHER  CASTINGS 


175 


This  figure  is  therefore  about  the  correct  amount  for  ingots  under 
conditions  similar  to  those  of  Mr.  Brineirs  experiments,  and  not 
far  different  in  any  event.  Mr.  Brinell  also  found  that  the  addi- 
tion to  the  steel  of  0.0184  per  cent,  of  aluminum  will  give  ap- 
proximately the  same  result  as  that  given  by  the  amount  of  man- 
ganese and  silicon  last  mentioned,  1.66. 

Location  of  Blow-holes.  —  The  number  and  size  of  blow-holes  is 
no  more  important,  however,  than  the  position  they  occupy  in  in- 
gots in  relation  to  the  external  surface.  Even  in  castings,  blow- 
holes, if  present,  should  be  deep-seated,  as  they  are  then  less  liable 
to  be  exposed  by  machine  work  performed  on  the  surface.  In  the 
case  of  ingots  the  deep-seating  is  of  still  greater  importance,  be- 
cause then  the  blow-holes  may  be  closed  up  before  they  have  an 
opportunity  to  break  through  to  the  surface  and  thus  become 
oxidized  on  their  interior.  The  normal  gases  in  blow-holes  are 
reducing  in  effect,  and  thus  the  interior  surfaces  of  the  holes  are 
bright  and  silvery  in  appearance  and  readily  weld  together ;  but  if 
they  become  oxidized  they  will  never  adhere  firmly.  For  instance, 
a  blow-hole  near  the  surface,  as  in  Figs.  120  and  122,  is  liable 


FIG.  120. —  SKIN 
BLOW-HOLES. 


FIG.    121.  — DEEP-SEATED 
BLOW-HOLES. 


FIG.    122. 


to  break  through  to  the  exterior  when  the  ingot  is  put  under  pres- 
sure. This  not  only  causes  a  crack  in  the  steel  but  allows  the  air 
to  oxidize  the  interior  of  the  hole  and  thus  prevent  the  crack  being 
welded  up  by  the  rolling.  It  is  not  at  all  uncommon  to  see  a 
number  of  these  openings  form  during  rolling  when  the  blow- 
holes are  near  the  surface. 

As  the  percentage  of  manganese  plus  5.2  times  the  percentage 
of  silicon  decreases  from  1.66,  the  blow-holes  become  correspond- 
ingly deeper-seated.  Finally  when  this  sum  becomes  as  low  as 
0.28,  the  blow-holes  are  harmlessly  located  in  the  interior.  It  is 


176  THE   METALLURGY   OF   IRON  AND   STEEL 

usually  impracticable,  however,  to  get  the  manganese  and  silicon 
as  low  as  this  in  steel,  because  manganese  is  needed  to  counteract 
the  bad  effect  of  sulphur  and  oxygen. 

The  location  of  the  blow-holes  is  also  very  largely  dependent 
upon  the  fluidity  of  the  metal  when  first  cast  into  the  molds.  The 
more  fluid  it  is,  other  things  being  equal,  the  nearer  will  the  blow- 
holes be  to  the  surface  of  the  solid  ingot.  On  the  other  hand,  if 
the  casting  temperature  is  too  low  there  will  be  a  dangerously  large 
number  of  blow-holes  in  the  steel  (see  Fig.  122),  because  it  solidifies 
so  quickly  that  very  little  opportunity  is  afforded  for  any  part  of 
the  dissolved  gases  to  escape.  The  fluidity  of  the  steel  depends 
partly  upon  its  temperature  and  partly  upon  the  amount  of  im- 
purities in  it.  For  instance,  pig  iron  is  fluid  at  a  temperature  at 
which  steel  is  solid;  high-carbon  steel  is  fluid  at  a  lower  temper- 
ature than  low-carbon  steel.  Therefore  every  different  kind  of 
steel  has  a  different  correct  casting  temperature;  but  we  have  al- 
ready learned  (p.  107)  how  to  determine  this  by  means  of  the  skull 
left  in  the  casting-ladle,  and  it  is  evident  that  this  test  applies 
equally  well  to  all  grades  of  steel.  It  is  to  be  observed  that  low- 
carbon  steel  suffers  greatly  from  blow-holes,  because  the  more  the 
carbon  the  less  oxidized  will  be  the  steel. 

Pipes.  —  When  steel  is  poured  into  a  mold,  it  forms  almost  im- 
mediately a  thin  skin  of  frozen  metal  against  the  cold  surface  of 
the  sand  or  iron.  The  radiation  of  heat  thereafter  necessarily 
takes  place  through  these  surfaces,  and  therefore  a  casting  will 
usually  complete  its  solidification  by  the  formation  of  thicker  and 
thicker  layers  of  solid  metal  around  all  the  sides.  The  top,  how- 
ever, will  usually  remain  molten  longer  than  the  rest  because  the 
hottest  metal  is  usually  at  this  point,  having  been  the  last  to  leave 
the  ladle,  and  also  because  the  heat  is  not  conducted  away  by  the 
air  as  fast  as  by  the  walls  of  the  mold.  This  is  especially  true  where 
the  casting  is  poured  into  an  iron  mold — for  example,  in  the  case 
of  ingots  (see  Fig.  123).  But  it  is  evident  that  at  some  period  a 
stage  will  be  reached  when  all  the  outside  of  the  ingot,  or  casting, 
will  be  covered  by  a  skin  of  solid  metal  while  the  interior  will  still 
be  liquid.  The  liquid  interior  will  continue  to  freeze  and  will,  at 
the  same  time,  contract.  The  result  will  be  the  shrinking  of  the 
molten  mass  away  from  the  solid  walls  and  consequently  the 
formation  of  a  cavity,  known  as  a  '  pipe/  in  the  interior.  This  pipe 
will  be  filled  with  the  gases  evolved  by  the  steel  during  solidification. 


DEFECTS   IN   INGOTS  AND  OTHER  CASTINGS 


177 


Professor  Howe  has  shown  that  the  volume  of  the  pipe  is  too  large 
to  be  accounted  for  altogether  by  the  shrinkage  of  the  steel  during 
solidification,  and  has  shown  that  the  rate  of  contraction  of  the 
inner  walls  of  the  ingot  being  greater  than  the  rate  of  contraction 
of  the  outer  walls,  a  virtual  expansion  of  the  outer  walls  is  caused 
and  a  consequent  enlargement  of  the  pipe.1 

The  portion  of  the  steel  containing  the  pipe  is  of  course  defective 
and  should  be  discarded  at  some  time  subsequent  to  casting.  In 
the  casting  of  ingots  the  upper  part,  which  contains  the  pipe,  is 


1 

^/^% 

- 

' 

=  | 

la 

Ij 

M^i 

Outside,  J, 
Solidifies 


Outside 
gets  Cool 


Pipe 
Begins 


Pipe 

Increases 


FIG.    123.  —  SOLIDIFICATION   OF  AN   INGOT. 


cut  off  during  the  rolling  or  forging  and  goes  back  to  the  furnace  to 
be  remelted  as  scrap.  In  the  casting  of  steel  castings  there  is  a 
large  adjunct  to  the  castings  situated  above  it,  and  so  regulated  in 
size  and  otherwise  that  it  freezes  after  the  casting  itself,  and  thus 
always  contains  a  supply  of  molten  metal  which  runs  down  and  fills 
any  cavity  that  forms  in  the  casting.  This  adjunct  is  cut  off  when 
the  casting  has  cooled.  In  other  words,  the  'riser'  or  'feeder/ as 
this  extra  part  is  called,  serves  the  same  purpose  for  a  steel  casting 
as  the  upper  part  of  an  ingot  does  for  the  ingot. 

Cast-iron  castings  do  not  form  a  pipe  under  ordinary  circum- 
stances, because  cast  iron  expands  during  solidification  on  account 
of  the  separation  of  graphite,  as  we  shall  learn  later.  Under  cer- 
tain circumstances,  however,  there  may  be  enough  difference  in 
expansion  between  the  inside  and  outside  of  cast-iron  castings  to 
produce  a  porous  spot  which,  while  not  exactly  a  pipe,  is  due  to 
similar  causes.  We  shall  discuss  this  matter  further  in  Chapter 
XII. 

1  No.  71,  page  183. 


178  THE  METALLURGY  OF   IRON  AND  STEEL 

•  Lessening  the  Volume  of  the  Pipe.  —  If  the  steel  were  poured 
into  the  mold  so  extremely  slowly  that  it  would  solidify  in  layers 
from  the  bottom  upward  there  would  be  no  pipe.  Therefore  one 
method  of  lessening  the  volume  of  the  pipe  is  by  slow  casting. 
We  have  already  noted  another  method,  namely,  permitting  a  small 
number  of  blow-holes  to  form,  which  causes  a  certain  amount  of  ex- 
pansion of  the  steel  during  solidification  and  thus  diminishes  its 
shrinkage.  Another  way  is  to  use  wide  ingots,  because  this  reduces 
the  difference  in  contraction  between  the  inner  and  outer  layers  of 
the  ingot,  which,  as  I  have  already  stated,  caused  a  virtual  expan- 
sion of  the  outer  walls  and  thus  enlarged  the  cavity.  Casting  in 
sand  molds  has  the  same  effect,  because  radiation  is  not  so  rapid 
through  sand  as  through  metal.  Still  another  method  is  to  pre- 
vent the  steel  forming  a  solid  skin  over  the  top  by  constantly 
stirring  and  breaking  it  up  with  an  iron  rod.  This  method  is 
often  resorted  to  with  the  risers  of  steel  castings,  with  very 
beneficial  results. 

Bottom  Casting.  —  In  the  case  of  steel  castings,  and  less  fre- 
quently in  the  case  of  ingots,  the  metal  is  poured  from  the  ladle 
into  a  runner  which  delivers  it  at  the  bottom  of  the  casting  (see 
Fig.  193,  p.  241).  With  steel  castings  this  is  often  necessary  in 
order  to  prevent  dirt  getting  into  the  casting.  It  also  has  a  similar 
effect  on  ingots,  because  it  prevents  slag  getting  into  the  molds 
and  also  prevents  metal  from  spattering  up  on  the  side  of  the  mold 
and  forming  what  is  known  as  a  'cold-shut/  that  is,  a  part  of  the 
metal  which  is  not  melted  in  with  the  rest.  In  both  cases,  how- 
ever, this  bottom  casting  has  the  effect  of  increasing  the  volume 
of  the  pipe  and  also  of  making  the  pipe  extend  deeper,  because  at 
the  end  of  casting  the  hottest  metal  is  at  the  bottom  instead  of  at 
the  top. 

Casting  with  the  Large  End  Up.  —  Risers  on  castings  are  al- 
most always  made  with  the  top  end  larger  than  the  bottom,  in 
order  that  the  pipe  may  be  less  in  volume  and  shorter  in  depth.  At 
steel- works,  however,  the  ingot  molds  are  always  tapered  slightly 
with  the  large  end  at  the  bottom,  in  order  that  the  mold  may  be 
easily  drawn  off  the  top  (see  p.  109) .  This  results  in  the  large  end 
of  the  ingot  being  down,  and  consequently  in  the  pipe  being  larger 
in  volume  and  very  much  greater  in  depth.1  Because  of  this 
advantage  Professor  Howe  has  proposed  certain  mechanical  ar- 

1  No.  72,  page  184. 


DEFECTS   IN   INGOTS  AND  OTHER  CASTINGS 


179 


rangements  by  which  the  ingot  may  be  cast  with  the  large  end 
upward.1 

Liquid  Compression  of  Ingots.  —  If  the  pipe  is  caused  by  the 
difference  in  expansion  between  the  inside  and  the  outside  of  an 
ingot,  it  is  evident  that  putting  sufficient  pressure  upon  the  outside 
when  the  walls  are  solid  but  the  interior  is  still  liquid  will  prevent 
the  formation  of  a  pipe.  Numerous  processes  have  been  devised 
for  effecting  this  liquid  'compression/  some  of  which  are  in  opera- 
tion at  steel-works  and  produce  ingots  that  are  entirely  free  from 
pipes.  In  Whitworth's  system  the  ingot  is  raised  and  compressed 
lengthwise  against  a  solid  ram  situated  above  it,  during  and  shortly 
after  solidification.2  In  Harmet's  method  the  ingot  is  forced  up- 
ward during  solidification  into  its  tapered  mold.2  This  causes  a 
large  radial  pressure  on  its  sides.  In  Lilienberg's  method  the 
ingots  are  stripped  and  then  run  on  their  cars  between  a  solid  and 
movable  wall.  The  movable  wall  is  then  pressed  against  one  side 
of  the  ingots.3 

Ingotism.  —  When  iron  and  steel  freeze  they  crystallize,  and 
these  crystals  grow  with  great  rapidity,  so  that  if  the  passage 
through  the  solidification  period  is  slow  they  will  attain  a  very 


FIG.    124.  —  INGOTISM. 

large  size.  This  formation  of  large  crystals  is  known  as  'ingotism/ 
It  is  especially  liable  to  occur  if  the  metal  is  cast  at  too  high  a 
temperature  or  is  allowed  to  cool  through  the  solidification  period 
1  See  No.  71,  page  183.  2  See  page  373  of  No.  1,  page  8.  *  See  No.  73,  page  184. 


180  THE  METALLURGY  OF   IRON  AND   STEEL 

at  too  slow  a  rate.1  In  the  case  of  steel,  ingotism  may  be  detected 
by  breaking  the  casting,  when  the  large  size  of  the  crystal  faces  or 
facets  may  be  observed. 

Damage  Due  to  Ingotism.  —  Large  crystals  always  produce 
weakness  and  loss  of  ductility,  for  the  large  crystals  do  not  adhere  to 
one  another  as  firmly  as  when  there  is  a  more  intimate  association ; 
consequently  steel  that  shows  ingotism  will  be  tender.  In  the  case 
of  steel  castings,  they  will  not  give  as  good  a  result  in  the  testing 
machine;  in  the  case  of  ingots  they  will  be  liable  to  tear  during  roll- 
ing or  under  the  hammer. 

Remedy  for  Ingotism.  —  Ingots  in  which  large  crystals  have 
formed  during  solidification  may  be  brought  to  a  high  degree  -of 
strength  and  ductility  by  forging  or  rolling,  because  the  mechanical 
work  crushes  the  crystals  and  reduces  them  to  a  smaller  size.  The 
work  must  be  done  very  carefully  at  first,  however,  or  cracks  will 
be  formed  that  are  not  afterward  welded  up.  Ingotism  in  steel 
castings  is  not  so  easy  to  cure;  indeed,  it  is  maintained  by  some 
authorities  that  its  bad  effects  are  never  entirely  obliterated.  I 
am  inclined  to  agree  with  this  opinion,  although  annealing  the  steel 
at  a  proper  temperature  (see  Chapter  XIV)  will  produce  a  very 
beneficial  effect. 

Segregation.  —  When  either  iron  or  steel  is  molten,  the  various 
impurities  are  dissolved  in  it,  and  some  of  them,  especially  carbon, 
phosphorus,  and  sulphur,  make  the  metal  more  fusible,  that  is,  they 
lower  its  melting-point.  But  the  impurities  are  not  as  soluble  in 
the  solid  metal,  and  therefore  tend  to  separate  on  solidification;  so 
it  can  readily  be  conceived  how  each  layer  that  freezes,  beginning 
at  the  outside,  rejects  some  of  its  impurities  to  be  dissolved  by 
the  still  liquid  mass  in  the  interior.  When  the  next  layer  freezes 
that  too  will  tend  to  reject  a  part  of  its  impurities  into  the  contigu- 
ous molten  layer,  and  thus  the  concentration  will  proceed  so  that  as 
a  general  thing  the  portion  of  the  metal  richest  in  impurities,  es- 
pecially in  carbon,  phosphorus,  and  sulphur,  will  be  that  which 
freezes  last.  With  ingots,  this  will  evidently  be  at  a  point  just  be- 
low the  bottom  of  the  pipe,  and  it  is  found  to  be  so  in  the  great 
majority  of  cases;  but  the  location  of  the  richest  segregate  is  very 

*In  the  case  of  cast  iron,  large  crystals  formed  during  solidification  pro- 
duce what  is  known  as  an  '  open  grain ' ;  we  shall  consider  this  more  particularly 
in  Chapter  XII.  The  name  'ingotism'  is  not  usually  applied  to  this  open 
grain  in  cast  iron. 


DEFECTS  IN   INGOTS  AND   OTHER  CASTINGS 


181 


liable  to  vary,  and  rules  can  only  be  used  for  general  guidance. 
For  example,  in  Fig.  125, l  the  most  impure  metal  is  found  at  a 
point  higher  than  the  bottom  of  the  pipe;  and  other  unexpected 

exceptions  occur.  In  the  case  of  iron 
and  steel  castings,  the  most  impure  point 
will  generally  be  near  the  top  of  the 
thickest  section  of  metal.  The  riser  is 
calculated  to  be  the  last  portion  to 
freeze  and  the  richest  segregate  should 
be  located  in  it. 

In  iron  castings  which  contained  on 
an   average  less  than  1  per  cent,  phos- 


— B 


Top  in  Ingot 


o  ®  o 


o 


.25  .20  .24  -26  .20 

O  O  O  O  O 

.24  .25  .22  .24  .24 

O  O  O  O  O 

.23  .23  .22  .23  .24 

O  O  O  •  ® 


FIG.  125.  —  LINES  OF 
EQUAL  CARBON- 
PERCENTAGE  IN 
A  STEEL  INGOT. 


FIG.  126.  —  CARBON-PENCENTAGE  AT 
DIFFERENT  PARTS  OF  A  STEEL 
INGOT. 


phorus   and   0.1    per   cent,  sulphur,  I  found   on  one  occasion   a 

segregated   portion  containing   1.856  per  cent,  phosphorus  and 

1  From  page  205  of  No.  71,  page  183. 


182 


THE   METALLURGY   OF    IRON   AND   STEEL 


0.144  per  cent,  sulphur;  and  on  another  occasion  I  found  one 
containing  2.43  per  cent,  phosphorus  and  0.236  per  cent,  sulphur. 
An  extreme  case  of  segregation  in  steel  is  shown  in  the  following 
analysis : l 


Carbon 
Per  cent. 

Silicon 
Per  cent. 

Manga- 
nese 
Per  cent. 

Phosphorus 
Per  cent. 

Sulphur 
Per  cent. 

Average 

0  24 

0   336 

0  97 

0.089 

0.07 

Segregate 

1  27 

0  41 

1.08 

0.753 

0.418 

Treatment  of  Segregated  Steel.  —  Segregation  cannot  be  pre- 
vented, although,  of  course,  it  seldom  takes  place  to  the  degree 
shown  in  the  extreme  cases  that  I  have  cited  above.  Nevertheless, 
there  are  always  certain  portions  of  the  ingot  or  casting  which  are 
richer  in  impurities  than  others.  An  attempt  is  made  to  get  this 
richer  portion  into  the  upper  part  of  an  ingot,  or  into  the  riser  of  a 
casting,  and  then  it  is  cut  off  when  the  ingot  is  rolled,  or  when  the 
riser  of  the  casting  is  removed.  It  is  therefore  advantageous  to 
cause  the  segregate  to  go  as  high  up  in  the  ingot  or  casting  as  pos- 
sible. Whatever  tends  to  raise  the  whole  pipe  higher  up  in  the  cast- 
ing would,  in  general,  tend  to  raise  the  segregate  also;  but  wide 
ingots,  or  ingots  cast  in  walls  with  low  conducting  power,  though 
they  tend  to  decrease  the  volume  of  the  pipe,  would  not  necessarily 
raise  the  segregate  to  a  higher  point.  Furthermore,  wide  ingots 
will  probably  have  a  much  greater  degree  of  segregation  than  nar- 
row ingots,  other  things  being  equal,  because  the  wider  the  ingot 
the  greater  will  be  the  number  of  layers  of  solidification,  and  con- 
sequently the  greater  concentration  of  impurities  in  the  center. 

Lessening  Segregation.  —  Benjamin  Talbot 2  has  shown  that 
quieting  the  steel  by  adding  aluminum  to  it  will  lessen  the  segre- 
gation. J.  E.  Stead  3  argues  that  this  result  is  due  to  the  branches 
of  crystals  (commonly  called  'fir-tree  crystals'),  which  grow  per- 
pendicularly to  the  cooling  surfaces  when  steel  solidifies  and  me- 
chanically entangle  some  of  the  impure  metal,  thus  preventing  it 
from  traveling  inward.  Professor  Howe  calls  this  type  of  freezing 
the  ' land-locking  type/  When  the  steel  is  violently  agitated  by 
the  escape  of  gas  its  rapid  movement  washes  off  the  fir-tree  crys- 

1  From  page  373  of  No.  1 ,  page  8.  2  Pages  204  to  223  of  No.  74. 

3  Pages  224  to  228  of  No.  74. 


DEFECTS   IN   INGOTS  AND   OTHER  CASTINGS  183 

tals  and  prevents  them  from  growing  out  into  the  liquid  mass  and 
entangling  the  impure  metal.  The  quietness  produced  by  alu- 
minum, however,  makes  this  growth  possible. 

Another  important  means  of  lessening  the  segregation  is  by 
making  ingots  narrow,1  that  is,  by  reducing  the  area  of  the  hori- 
zontal cross-section;  but  this  is  often  difficult  of  accomplishment. 
For  example,  if  we  cast  fifty  tons  of  open-hearth  steel  out  of  one 
ladle,  it  will  take  a  very  long  time  to  cast  all  of  this  into  small  in- 
gots, and  therefore  the  first  ingots  cast  will  be  too  hot  or  else  the 
last  ingots  will  be  too  cold.  There  is  a  difference  of  opinion  as  to 
whether  or  not  rapid  cooling  decreases  or  increases  the  degree  of 
segregation,  and  it  seems  probable  that  it  acts  in  both  directions, 
sometimes  prevailing  one  way  and  sometimes  in  the  opposite.  On 
first  thought  it  would  seem  that  slow  cooling  must  necessarily  in- 
crease segregation,  because  it  would  allow  more  time  for  the  im- 
purities to  separate  from  one  layer  of  metal  and  dissolve  in  the  next. 
On  the  other  hand,  slow  cooling  also  favors  the  growth  of  the  fir- 
tree  crystals,  and  therefore  opposes  segregation.  It  does  not  seem 
possible,  at  the  present  time,  to  tell  under  what  conditions  we 
should  have  the  one  influence  prevailing  or  the  other. 

It  seems  to  be  pretty  well  established  that  the  greater  the  per- 
centage of  impurities  present  the  greater  will  be  the  extent  of  the 
segregation.  Therefore  high-carbon  steel  should  be  cast  with  due 
care  and  narrow  ingots  used  wherever  possible.  Generally  when 
the  phosphorus  and  sulphur  are  low  (say,  not  more  than  0.05  per 
cent,  each),  much  segregation  is  not  liable  to  occur,  especially  in 
low-carbon  steels. 


REFERENCES  ON  DEFECTS  IN  INGOTS 

70.  C.  A.  Caspersson.     Reviewed  by  Richard  Akerman.     "The 

Influence  of  the  Temperature  of  the  Bessemer  Charge  on 
the  Properties  of  the  Steel  Ingots."  Stahl  und  Eisen,  1883, 
pages  71-76. 

71.  Henry  M.  Howe.     "Piping  and  Segregation  in  Steel  Ingots." 

Transactions,  American  Institute  of  Mining  Engineers, 
1907.  Advance  proof. 

1  Some  metallurgists  disagree  with  this  and  believe  that  the  large  ingots 
do  not  segregate  so  much.  Nevertheless,  I  am  inclined  to  think  that  the 
greater  weight  of  evidence  is  against  them  in  this  contention. 


184  THE  METALLURGY  OF   IRON  AND  STEEL 

72.  Henry  M.  Howe  and  Bradley  Stoughton.     "The  Influence 

of  the  Conditions  of  Casting  on  Piping  and  Segregation,  as 
Shown  by  Means  of  Wax  Ingots/'  Transactions,  American 
Institute  of  Mining  Engineers,  1907.  Advance  proof. 

73.  N.    Lilienberg.     "Piping    in    Steel    Ingots. "     Transactions, 

American  Institute  of  Mining  Engineers,  vol.  xxxvii,  1906, 
pages  238-247. 

74.  Benjamin  Talbot.     "Segregation  in  Steel  Ingots."     Journal, 

Iron  and  Steel  Institute,  No.  11,  1905,  pages  204-247. 

75.  N.     Lilienberg.     "The    Compression    of    Semi-liquid    Steel 

Ingots."     Journal  of  the  Franklin  Institute,  February,  1908. 

76.  E.  von  Maltitz.     "Blowholes  in  Steel  Ingots."     Transactions, 

American  Institute  of  Mining  Engineers,  vol.  xxxviii,  1907, 
pages  412-447. 


VIII 
THE  MECHANICAL   TREATMENT   OF   STEEL 

METALS  may  be  shaped  either  by  pouring  them  whilst  molten 
into  a  mold,  as  described  in  the  following  chapter,  or  by  mechanical 
pressure.  The  choice  of  the  casting  or  the  mechanical  method  of 
shaping  will  depend  on  the  size  and  form  of  the  finished  product 
and  the  purpose  for  which  it  is  intended.  Some  shapes  must  be 
produced  by  casting,  because  they  are  either  too  intricate  or  too 
large  to  be  shaped  by  pressure;  others  must  be  produced  by  pres- 
sure, because  the  service  in  which  they  are  to  be  used  demands 
the  higher  strength  and  ductility  which  mechanical  work  pro- 
duces. Between  these  two  classes,  however,  is  a  large  number  of 
forms,  each  of  which  is  a  study  by  itself.  Financial  considera- 
tions will  govern  in  some  cases,  and  the  importance  of  quality 
in  others.  The  advantage  of  quality  is  usually  with  the  pressed 
material. 

Effect  of  Work.  —  Mechanical  work  will  multiply  the  strength 
of  steel  from  two  to  five  times.  In  order  to  accomplish  as  much  as 
this,  however,  it  is  necessary  to  reduce  the  material  to  very  small 
sizes,  in  order  that  the  beneficial  effect  of  the  kneading  action  may 
extend  throughout  the  mass,  and  to  finish  the  work  cold,  in  order 
that  the  metal  may  have  no  opportunity  to  recrystallize.  The 
ductility  also  will  be  increased  at  first  by  working,  but  again  de- 
creases if  the  metal  is  worked  cold.  The  increase  in  strength  and 
ductility  is  due  (1)  to  the  closing  up  of  blow-holes,  both  large  and 
small,  which  are  almost  all  welded  together  under  pressure  at  high 
temperatures,  unless  they  are  near  enough  to  the  surface  to  be- 
come oxidized  inside,  and  (2)  to  increasing  the  cohesion  and  ad- 
hesion of  the  crystals.  The  first  effect  is  contributive  both  to 
strength  and  ductility,  while  the  second  is  chiefly  contributive  to 
strength,  and,  if  excessive,  will  greatly  diminish  ductility.  Both 
increase  the  specific  gravity  and  hardness  of  the  metal,  and  are 
more  effective  in  these  respects,  as  well  as  in  increasing  strength, 
if  hot  work  is  followed  by  cold  work. 

185 


186 


THE   METALLURGY  OF   IRON   AND   STEEL 


Crystallization  of  Steel.  —  Metals  are  crystalline  substances, 
the  individual  components  arranging  themselves  in  regular  forms 
unless  opposed  by  the  rigidity  of  the  mass  in  which  they  form. 
Indeed,  the  metallic  crystals  grow  with  astonishing  rapidity  when 
the  metal  crystallizes  from  the  molten  state  (i.e.,  solidifies),  or 
even  when  it  is  in  a  mobile  condition  (i.e.,  at  temperatures  near 
or  above  a  red  heat).  Once  crystals  have  formed  they  cannot  be 
reduced  in  size  except  by  annealing  (see  Chapter  XIV) ,  or  by  break- 
ing them  up  with  mechanical  crushing.  These  facts  are  important, 
because  large  crystals  do  not  adhere  to  each  other  firmly,  and 
thus  they  cause  a  weak  and  brittle  mass.  Iron  and  steel  follow 
the  same  laws  as  other  metals  in  these  respects. 

Effect  of  Strain.  —  When  a  metal  is  strained,  the  crystals  first 
stretch,  and  the  amount  of  this  stretching  is  directly  proportional 
to  the  strain;  when  the  metal  is  relieved,  the  crystals  and  the  mass 


STRAIGHT  SLIP  BANDS 

IN  WROUGHT  IRON 
MAGNIFIED  60  DIAMETERS. 

Unetched. 
(William  Campbell.) 


CURVED    SLIP    BANDS 

IN  WROUGHT  IRON 
MAGNIFIED  60  DIAMETERS. 

Unetched. 
(William  Campbell.) 


as  a  whole  return  to  the  original  dimensions.  If  the  strain  is 
greater  than  the  '  elastic  limit/  however,  the  crystals  yield,  and 
the  particles  composing  them  slip  along  the  cleavage  planes,  so 
that  a  permanent  deformation  or  extension  occurs  in  the  direction 
of  the  strain.  This  'elongation'  is  accompanied  by  a  'reduction 
in  cross-sectional  area/  and  gives  warning  that  the  material  is 
suffering  from  excessive  strain.  The  extent  to  which  these  two 


THE  MECHANICAL  TREATMENT  OF   STEEL  187 

forms  of  distortion  precede  rupture  is  usually  taken  as  the  meas- 
ure of  the  'ductility'  of  the  metal. 

Rationale  of  the  Effect  of  Work.  —  Mechanical  pressure  upon  a 
metal  crushes  the  crystals,  mixes  them  intimately  together,  and 
breaks  up  the  cleavage  planes  along  which  they  would  yield.  If 
the  work  is  finished  above  a  red  heat  when  the  mass  is  still  mobile, 
the  crystals  reform  to  a  certain  extent,  decreasing  the  strength. 
The  elastic  limit  of  a  structural  steel  rolled  in  this  way  will  be  a 
little  more  than  one-half  its  ultimate  strength.  If  the  work  con- 
tinues while  the  metal  is  cold,  there  is  no  opportunity  for  the  re- 
formation of  the  crystals,  and  the  strength,  hardness,  and  brittle- 
ness  are  much  increased. 

Methods  of  Applying  Pressure.  —  Aside  from  the  differences  of 
hot  and  cold  working,  the  mechanical  pressure  may  be  exerted  in 
one  of  three  ways:  (1)  Instantaneously,  by  a  blow,  in  which  method 
the  pressure  is  relieved  before  the  metal  has  fully  yielded  to  it; 
(2)  more  slowly,  by  rolling  or  wire-drawing,  in  which  the  pressure 
is  relieved  almost  as  soon  as  the  metal  has  yielded  to  it;  and  (3) 
slowest,  by  presses,  in  which  the  pressure  remains  for  a  second  or 
so  after  the  metal  has  yielded. 


THE  FORGING  OF  METALS 

The  instantaneous  application  of  pressure  is  man's  first  method 
of  shaping  metals  and  is  accomplished  by  a  blow  from  a  falling 
weight,  frequently  aided  by  some  other  force.  Examples  of  the 
first  practice  are  found  at  the  present  time  in  the  helve-hammer 
used  at  many  small  forges  and  steel-works.  After  the  introduc- 
tion of  steam,  however,  this  was  used  to  raise  the  weight,  and  very 
soon  steam-power  was  employed  not  only  to  raise  the  weight  but 
also  to  force  it  downward  for  the  blow,  whose  momentum  was  thus 
greatly  increased.  Hammers  of  this  type,  which  is  now  the  most 
prevalent,  have  been  built  capable  of  delivering  a  blow  estimated 
as  equivalent  to  150  tons  weight.  Such  large  sizes  are  not  now 
-approved  of,  however,  because  of  the  inordinate  expense  for  foun- 
dations, which  must  be  deep  and  powerful  in  order  to  take  up  the 
force  of  the  blow,  while  the  constant  jarring  disturbs  the  founda- 
tions and  alinement  of  machinery,  even  at  distant  parts  of  the 
plant.  For  very  heavy  forging  work,  such  as  armor-plate,  etc., 


188 


THE   METALLURGY   OF   IRON  AND   STEEL 


the  hydraulic  press  is  therefore  preferred,  and  hammers  are  not 
often  built  in  sizes  above  30  or  50  tons. 

Effect  of  Hammering.  —  A  blow  creates  in  a  metal  practically 
nothing  but  compressive  strains,  which  act  chiefly  in  the  vertical 
direction,  and,  by  transmission,  in  the  two  horizontal  directions. 
Because  the  pressure  is  relieved  almost  as  soon  as  felt,  the  amount 


FIG.    127. —  STEAM   HAMMER. 


of  yield  to  it  is  not  great  in  proportion  to  its  force,  and  therefore  it 
takes  more  pressure  to  accomplish  a  result  than  would  be  the  case 
if  the  application  was  slower.  This  makes  hammering  a  slow 
process  of  reduction,  but  results  in  a  better  and  more  uniform 
working  of  the  crystals,  which  is  one  of  the  chief  reasons  for  the 
superiority  of  hammered  over  rolled  material.  On  the  other  hand, 


THE  MECHANICAL  TREATMENT  OF   STEEL  189 

the  effect  of  forging  extends  only  1  or  2  inches  beyond  the  upper 
and  lower  surfaces.  Another  and,  perhaps,  even  more  potent 
reason  is  the  exact  control  of  the  operation  which  can  be  exercised 
by  the  expert  forger,  and  more  especially  his  control  over  the  tem- 
perature at  which  the  work  is  finished,  and  over  the  varying  force 
of  pressure  applied  at  different  stages  and  temperatures. 

Finishing  Temperatures  for  Forging.  —  Forging  seldom  con- 
tinues after  the  red  heat  is  lost,  but  the  exact  temperature  will 
depend  upon  the  article  and  the  properties  which  it  is  desired  to 
have.  The  colder  it  is  finished  the  closer  to  the  exact  size  required 
it  can  be  made,  because  it  has  less  shrinkage  to  undergo;  but  it 
will  also  be  harder,  less  ductile  and  stronger.  The  relation  be- 
tween the  finishing  temperature  of  mechanical  work  and  the  critical 
points  of  steel  will  be  discussed  in  Chapter  XIV. 

Drop-Forging.  —  There  is  a  large  variety  of  articles,  such  as 
parts  of  machinery,  hammer-heads  and  similar  tools,  which  are 
formed  by  the  process  known  as  'drop-forging.'  In  this  operation 
a  piece  of  metal  of  the  desired  size  is  forged  by  repeated  blows 
between  a  lower  die,  upon  which  it  rests,  and  an  upper  die  attached 
to  the  head  of  the  hammer.  These  two  dies  are  made  in  the  de- 
sired form  of  the  finished  article,  and  the  metal  is  squeezed  into 
them  until  it  has  assumed  the  proper  shape.  Sometimes  several 
pairs  of  dies  are  necessary  to  complete  the  finished  shape  (see  Fig. 
129) .  Drop-forgings  are  directly  comparable  with  steel  castings,  to 
which  they  are  superior  in  quality  on  account  of  the  beneficial 
effect  of  the  working.  To  be  economically  made,  they  must  be 
ordered  in  large  quantities,  so  that  it  will  pay  to  make  the  costly 
dies  of  hardened  steel  —  often  an  alloy.  Even  then,  castings  are 
usually  cheaper,  though  sometimes  forgings  are  still  preferred  on 
account  of  their  quality.  There  are  cases,  however,  in  which 
drop-forgings  may  be  made  more  cheaply,  either  because  the 
shape  is  one  that  lends  itself  to  rapid  production  in  this  way,  or 
because  it  is  one  liable  to  cheeking,  or  requiring  a  large  riser,  if  cast. 

Forging  Bars.  —  Crucible-steel  ingots  are  often  forged  out  into 
bars  for  the  market,  because  the  material  will  bring  a  price  high 
enough  to  pay  for  the  superior  method  of  working  it.  The  ingot, 
after  the  top  third  has  been  broken  off  to  remove  the  pipe  and 
segregate,  is  heated  to  a  bright-red  heat,  out  of  contact  with  the 
flame  and  fuel,  and  then  tilted  down  under  a  hammer  of  about  10  to 
15  tons  size  until  it  is  about  one-half  as  large  on  the  sides  and  four 


190 


THE  METALLURGY  OF   IRON  AND   STEEL 


times  as  long.  The  piece  is  held  in  a  handle  which  fits  over  one  end 
of  it,  and  usually  a  second  heating  is  necessary  before  both  ends  are 
down  to  the  correct  size.  One  end  is  then  reheated  and  drawn 


FIG.    128. —  SOME   AUTOMOBILE   DROP-FORCINGS. 

down  to  a  bar  of  the  desired  size,  under  the  same  hammer,  or  under 
one  of  less  weight,  and  the  long  bar  is  then  used  as  a  handle  while 
the  other  end  undergoes  heating  and  reduction.  The  finished  size 
is  produced  by  light  taps  of  the  hammer  just  before  the  blue  heat 


FIG.   129.  — SOME  STAGES   IN  THE  MAKING  OF  A  DROP-FORGING. 

191 


192  THE  METALLURGY  OF   IRON  AND   STEEL 

appears,  and  often  a  piece  of  cold  steel  is  laid  beside  it  on  the  anvil 
to  more  correctly  arrest  the  downward  blow.  The  finished  bar 
will  be  so  straight  and  true  as  to  lead  one  to  believe  that  it  was 
produced  by  drawing  through  a  die,  or  rolling  in  grooved  rolls. 
Sometimes  it  is  finished  in  a  square  shape,  and  sometimes  as  an 
octagon,  by  turning  it  upon  the  corners  and  drawing  them  down. 

Forging  Razors.  —  Flat  bars  for  razor  stock,  made  of  cemented 
steel  melted  in  crucibles  without  additional  carbon,  are  produced 
in  a  manner  similar  to  that  outlined  above,  and  then  forged  down 
by  hand  to  the  rough  size  of  a  razor.  They  are  then  stamped  with 
the  appropriate  name  and  mark,  drilled  with  a  hole,  heated  to  the 
correct  temperature  and  hardened  in  water,  after  which  the  temper 
is  drawn  to  the  light  or  medium  straw  color  (see  page  387).  The 
exact  shape  is  then  produced  by  grinding,  care  being  taken  not  to 
heat  the  razor  during  this  operation,  lest  it  be  tempered  thereby, 
and  the  blade  polished  and  fitted  with  a  handle. 

Forging  Cannon.  —  Large  cannon  tubes  are  made  from  open- 
hearth  steel  ingots  weighing  perhaps  65  tons  or  so,  more  than  one- 
half  of  which  is  discarded  or  'scrapped'  during  the  process.  In 
France  and  Germany,  cannon-tube  ingots  have  been  made  of 
crucible  steel  by  pouring  many  crucibles  into  one  mold,  but  the 
expense  and  the  liability  to  heterogeneity  because  of  the  many 
small  units  is  believed  to  outweigh  the  advantages  due  to  the 
quality  of  steel,  which  is  superior  on  account  of  its  process  of 
manufacture.  The  heating  of  the  ingots  must  be  done  with  great 
care,  lest  a  crack  or  hollow  be  formed  by  too  rapid  expansion  or 
by  the  expansion  of  the  outside  away  from  the  interior.  More- 
over, as  reducing  a  flame  as  possible  must  be 
maintained,  lest  the  carbon  be  oxidized  in  the 
outer  layers  of  steel  during  the  many  hours 
required  to  attain  the  bright-red  heat  neces- 
sary. Ingots  of  the  form  shown  in  Fig.  130 
are  usually  employed,  and  those  cast  in  sand 
molds  are  preferred  because  they  are  not  liable 
to  contain  surface  cracks  produced  by  tearing 
FIG.  130.  the  steel  when  the  iron  mold  is  withdrawn. 

Only  one  end  of  the  ingot  projects  into  the 
furnace,  and  when  the  desired  temperature  is  reached,  the  handle 
or  'porter  bar7  is  fitted  over  the  cool  end,  and  the  crane  which 
supports  this  transfers  the  whole  over  to  the  hammer. 


THE   MECHANICAL  TREATMENT    OF  STEEL  193 

By  the  time  the  heavy  blows  from  a  hammer  of  perhaps  75 
tons  force  have  effected  a  certain  reduction,  the  ingot  must  go 
back  to  the  furnace  for  another  heating  of  about  an  hour  or  so,  and 
this  reheating  is  necessary  at  intervals.  When  the  top  end  of  the 
ingot  has  been  drawn  down  to  a  convenient  size,  this  is  used  as  a 
handle  to  the  other  end,  which  is  to  make  the  completed  cannon 
tube,  and  not  more  than  the  lower  two-thirds  of  the  original  ingot 
is  allowed  to  be  present  in  the  tube  at  the  finish  of  the  forging 
operation.  The  blows  are  delivered  on  all  sides  of  the  ingot  in 
order  that  the  center  of  the  tube  shall  be  the  same  as  the  center 
of  the  original  ingot,  for  this  center  portion  is  to  be  drilled  out 
in  the  subsequent  operations,  and,  as  we  have  already  seen,  the 
center  of  the  ingot  is  of  looser  texture  and  contains  more  of  the 
segregate. 

After  the  inner  tube  is  forged,  an  outer  tube  is  produced  in  a 
similar  manner,  but  of  larger  size,  so  that  it  may  be  bored  out  to 
fit  over  the  carefully  turned  inner  tube.  After  the  boring  the 
outer  tube  is  too  small  to  pass  over  the  inner  one,  and  it  is  therefore 
heated  to  a  temperature  of  about  280°  C.  (550°  F.)  in  a  tall  vertical 
furnace,  which  expands  it  so  that  it  may  be  passed  over  the  inner 
tube  and  '  shrunk'  upon  it,  greatly  increasing  its  compactness  and 
reinforcing  it  against  the  tremendous  strains  it  is  subjected  to  in 
service.  Cannons  are  now  frequently  forged  under  presses  instead 
of  under  hammers. 


THE  REDUCTION  OF  METALS  IN  ROLLS 

If  two  rolls  rotating  as  shown  in  section  in  Fig.  131  be  made  to 
grip  a  piece  of  metal,  A,  they  will  drag  it  between  them  and  force 
it  out  on  the  other  side  reduced  in  thickness.  The  metal  between 
the  points  0  0  and  N  N  is  being  compressed  vertically,  while  its 
outer  layers  are  suffering  tension.  In  the  case  of  a  deep  section, 
the  unequal  strain  is  liable  to  tear  the  steel  (see  Fig.  165).  At  the 
points  N  N  the  metal  is  being  forced  back  upon  itself.  The 
mechanical  pressure  is  therefore  not  as  uniform  as  in  hammering, 
and  acts  for  a  longer  period  of  time.  Reduction  can  only  take 
place  vertically,  as  in  forging,  there  being  always  a  certain  amount 
•of  expansion  sidewise,  and  a  large  amount  of  extension  in  length. 
The  metal  at  the  points  N  N  being  forced  backward,  and  that  at 
the  points  0  0  being  forced  forward,  the  ends  of  the  rolled  section 


194 


THE  METALLURGY   OF   IRON  AND   STEEL 


assume  a  shape  somewhat  like  that  shown  in  Figs.  132  and  133, 
when  the  outside  of  the  piece  is  very  hot.  The  reduction  in 
area  at  each  'pass'  will  vary  between  5  and  50  per  cent,  of  the 
original,  and  the  work  is  very  rapid.  For  example,  a  railroad  rail 


FIG.    131. 

may  be  produced,  from  an  ingot  having  a  section  18  in.  square,  in 
22  passes,  varying  in  amount  of  vertical  squeeze  from  8  to  52  per 
cent.,  only  about  five  minutes  being  required  for  the  whole  opera- 
tion, the  piece  traveling  through  some  of  the  passes  at  a  rate  of  ten 
miles  per  hour,  and  not  being  reheated  after  the  ingot  comes  to  the 


FIG.  132.  — SHAPE  OF  ENDS  OF 
ROLLED  METAL  WHEN  THE 
INSIDE  IS  THE  HOTTER. 


FIG.  133.  — SHAPE  OF  ENDS  OF 
ROLLED  METAL  WHEN  THE 
OUTSIDE  IS  THE  HOTTER. 


first  pair  of  rolls.  Some  American  rolling-mills  produce  about  a 
mile  of  single"  rail  per  hour  for  24  hours  a  day  and  25  days  per  month. 
The  temperature  at  which  the  rolled  material  is  finished  is  gaged 
with  much  less  accuracy  than  in  forging  operations,  and  is  always 


THE  MECHANICAL  TREATMENT  OF  STEEL  195 

too  high  for  the  best  quality  of  the  steel,  because  economy  of  power 
urges  the  manufacturer  to  work  the  metal  hot. 

Pull-Over  Mill.  —  In  a  single  pair  of  rolls,  such  as  shown  in 
Fig.  131,  the  metal,  after  passing  between  them  once,  must  be 
handed  or  pulled  over  the  top  of  the  mill,  to  be  fed  in  for  a  second 
pass.  This  type  of  train  is  known  as  a  'pull-over'  or  'pass-over' 
mill.  It  can  be  used  only  for  shapes  small  in  size  and  that  can  be 
handled  readily,  and  the  action  is  slower  than  in  a  continuous 
operation,  such  as  in  a  'three-high  mill.'  The  pull-over  mill  is 
simple  and  cheap  to  construct  and  operate,  and  is  used  especially 
for  the  rolling  of  plates  and  shapes  from  crucible  steel,  whose  high 
price  renders  it  less  important  to  seek  rapid  output.  It  is  also 
used  very  largely  for  the  rolling  of  steel  to  be  used  for  tinplate. 
The  upper  roll  is  adjustable,  so  that  any  thickness  may  be  pro- 
duced. 

Multiple-Ply  Plate,  etc.  —  Three-ply  plate  for  plowshares, 
and  five-ply  plates  or  bars  for  burglar-proof  safes  and  jail  bars, 
are  often  made  in  this  type  of  mill.  We  first  roll  independently 
thin  plates  of  high-carbon,  crucible,  chrome  steel  (or  an  equiva- 
lent alloy  steel  capable  of  becoming  very  hard  upon  quenching  in 
water  from  a  red  Heat),  and  thicker  plates  of  wrought  iron.  For  a 
plowshare,  a  plate  of  wrought  iron  will  then  be  sandwiched  be- 
tween two  plates  of  chrome  steel,  tied  into  a  bundle  with  wire,  and 
raised  to  a  welding  heat.  The  wire  burns  off  in  the  furnace,  but 
the  bundle  is  grasped  with  a  pair  of  tongs  and  fed  into  a  pair  of 
plain  rolls,  where  it  is  welded  into  a  plate  of  three-ply  steel  which 
is  reduced  to  a  thickness  of  a  little  over  a  quarter  of  an  inch.  This 
plate  is  trimmed  to  about  the  desired  size  and  shape  and  then 
hardened  and  used  for  a  plow,  the  hard  outer  layers  resisting  the 
wear  of  service,  and  the  ductile  core  resisting  the  shocks  which 
would  shatter  the  brittle  outside.  For  safes  and  jail  bars  we  have 
an  inner  layer  of  wrought  iron,  then  two  layers  of  chrome  steel, 
and  then  two  layers  of  wrought  iron,  welded  together  and  then 
hardened.  A  burglar  can  neither  drill  through  this,  on  account  of 
the  hardened  chrome  steel,  nor  break  it  with  a  sledge,  on  account 
of  the  ductile  iron,  which  will  not  be  hardened  by  the  quenching. 

Three-High  Mills.  —  When  a  piece  is  passed  over  a  two-high 
mill,  it  is  often  rested  upon  the  top  of  the  upper  roll,  whose  travel 
assists  somewhat  in  the  transfer.  While  watching  this  operation 
at  the  Cambria  Iron  Company's  mill  in  1857,  John  Fritz  con- 


196 


THE   METALLURGY   OF   IRON   AND   STEEL 


ceived  the  idea  of  the  three-high  mill,  which  is  shown  in  section 
in  Fig.  134.  It  will  be  seen  that  passing  the  piece  over  the  top  of 
the  middle  roll  in  this  mill  will  result  in  its  receiving  work,  and 
thus  the  output  of  the  mill  will  be  increased.  At  the  present  time 
the  great  bulk  of  the  tonnage  of  steel  and  wrought  iron  produced, 
consisting  of  structural  shapes,  railroad  rails,  plates,  wire  rods, 


FIG.   134. 

billets  and  bars,  is  finished  in  this  type  of  mill.  The  output  is 
large,  because  the  rolls  can  be  run  very  fast  indeed  (rod  mills  run- 
ning 600  to  1200  revolutions  per  minute  and  sometimes  passing  the 
rod  through  at  the  rate  of  half  a  mile  a  minute  in  American  prac- 
tice 1),  and  two  or  more  pieces  maybe  passing  through  at  the  same 
time.  The  disadvantage  of  the  three-high  mill  is  the  power  neces- 

1  The  reason  for  this  rapid  rolling  is  not  only  large  product,  but  that  the  thin 
rods  may  not  radiate  their  heat  during  the  operation  and  thus  be  finished  too 
cold.  This  rapid  work  actually  raises  the  heat  of  the  metal  faster  than  it  can 
be  radiated,  and  rods  are  hotter  at  the  end  than  at  the  beginning  of  the  rolling. 


THE   MECHANICAL   TREATMENT   OF   STEEL  197 

sary  to  raise  large  weights  up  to  pass  over  the  middle  roll.  Most 
Bessemer  ingots  are  cast  two  tons  or  more  in  weight,  and  most 
open-hearth  ingots  from  three  tons  to  ten  or  more  tons. 

Reversing  Mills.  —  Therefore  ingots  are  often  '  cogged'  in  two- 
high  reversing  mills  to  avoid  this  consumption  of  power.  More- 
over, the  two-high  mills,  which  have  an  adjustable  upper  roll,  have 
the  advantage  of  being  able  to  work  an  ingot  gently  at  first,  in 
case  it  shows  a  tendency  to  be  '  tender/  that  is,  to  crack  in  spots 


FIG.    135.  —  THREE-HIGH   MILL. 

when  the  pressure  is  applied.  Three-high  mills  may,  however,  also 
have  an  adjustable  middle  roll,  and  plate  mills  are  frequently  made 
in  this  way.  The  disadvantages  of  the  two-high  reversing  mill  are 
its  slowness  and  the  severe  strain  on  the  engines,  which  are  often 
reversed  while  running  full  speed. 

Universal  Mill.  —  During  the  rolling  of  metal  there  is  a  cer- 
tain amount  of  expansion  sidewise,  which  gives  the  piece  a  cross- 
section  somewhat  bulging  on  the  sides,  and  makes  the  edges 
uneven,  unless  the  rolls  have  collars  which  form  a  groove  through 
which  the  metal  passes.  In  1855  R.  M.  Daelen,  at  Hoerde,  Ger- 
many, devised  a  mill  in  which  even  edges  could  be  produced  at  any 
width  by  having  an  auxiliary  pair  of  vertical  rolls,  between  which 
the  piece  passes  immediately  after  it  emerges  from  the  horizontal 
rolls.  These  vertical  rolls  are  adjustable  to  any  width  up  to  the 
capacity  of  the  mill,  and  give  only  enough  pressure  to  keep  the 
edges  even  without  producing  any  reduction.  They  are  usually 
made  to  rotate  with  a  surface  velocity  greater  than  that  of  the  hori- 


200  THE  METALLURGY   OF   IRON   AND   STEEL 

zontal  rolls,  so  as  to  prevent  the  serious  buckling  that  would  take 
place  if  the  conditions  were  reversed.  As  this  tension  is  not  good 
for  the  edges  of  the  metal  and  wears  out  the  vertical  rolls,  some 
mills  have  independent  control  of  drive  for  each  pair  of  rolls,  and 
others  have  friction-clutches  connected  with  the  vertical  rolls, 
which  allow  them  to  run  faster  if  pushed  by  the  metal,  but  ordi- 
narily run  them  at  a  slower  speed.  Universal  mills  are  made 
two-high  or  three-high,  and  with  vertical  rolls  on  one  or  on  both 
sides  of  the  horizontal  rolls.  With  the  two-high  mills  (which  are, 
of  course,  reversing),  there  is  one  set  of  vertical  rolls.  Slabbing- 
mills  are  usually  made  this  way.  With  three-high  mills,  there  is 
a  pair  of  vertical  rolls  on  both  sides  of  the  horizontal  rolls.  Plate- 
mills  are  sometimes  of  this  kind.  In  England,  the  Universal  mill 
is  not  in  favor,  as  rolling-mill  managers  believe  that  the  faster  work 
of  simple  mills  more  than  makes  up  for  the  necessity  for  changing 
grooved  rolls  at  intervals  when  a  new  width  is  to  be  produced. 


PARTS  OF  ROLLING  MILLS 

Rolls.  —  Rolls  may  be  plain  cylinders,  by  which  plates  and 
rectagonal  shapes  are  produced,  or  they  may  be  cylinders  with 
'collars'  at  intervals,  as  shown  in  Fig.  138,  in  which  large  rectagonals 
with  even  edges  may  be  produced ;  and  the  collars  may  be  on  both 
rolls,  giving  an  'open  pass/  or  may  be  on  only  one  roll  and  extend 
into  grooves  on  the  other  roll,  as  shown  in  Fig.  139,  giving  a '  closed 
pass.'  With  open  passes,  the  collars  cannot  be  made  to  quite 
touch,  hence  the  name;  and  the  pressure  may  squeeze  some  metal 
between  them,  forming  a  'fin'  along  the  side  of  the  piece.  This 
results  from  'overfilling  the  pass.'  The  closed  pass  makes  the 
upper  roll  weaker,  and  there  is  also  a  liability  of  the  metal  becom- 
ing wedged  tightly  between  the  collars  and  thus  drawn  all  the  way 
around  the  roll,  with  the  result  that  something  will  be  broken. 
Wedge-shaped  grooves  may  be  cut  in  the  rolls,  producing  the 
'diamond'  pass,  in  which  small  squares  are  made  (see  Fig.  139);  or 
oval  grooves  make  nearly  round  bars  which  are  finished  round  in 
the  last  pass  with  almost  no  draft.  Other  forms  of  passes  are 
shown  in  Figs.  139  and  165.  In  case  rolls  are  weakened  by  deep 
cutting,  as  shown  in  Fig.  139,  they  may  be  strengthened  by  stiffen- 
ers,  D,  while  long  rolls  for  producing  wide  plates  are  sometimes 


THE   MECHANICAL  TREATMENT   OF   STEEL 


201 


stiffened  by  an  idle  roll  running  on  top,  lest  the  springing  of  the 
roll  make  the  plate  thicker  in  the  middle  than  at  the  edges. 

Cast-iron  versus  Steel  Rolls.  —  Cast-iron  rolls  are  chilled  upon 
the  outside  so  as  to  produce  a  surface  layer  of  white  iron  (see  Fig. 
264),  which,  after  turning  in  a  lathe,  makes  a  very  smooth  surface 
for  rolling  and  is  especially  advantageous  for  finishing-mills.  They 
are  not  so  good  for  the  mills  which  do  preparatory  work,  however, 
because  they  are  not  so  strong,  and  because  in  preparatory  work  we 


FIG.    138.  —  CC  =  COLLARS.     W  =  WOBBLERS. 

want  a  rough  surface  to  assist  in  gripping  the  metal  and  drawing 
it  through.  Furthermore,  they  cost  more  to  turn  to  the  desired 
shape,  and  they  cannot  be  turned  down  many  times  (see  page  203) , 
lest  we  get  below  the  '  chill/  The  greater  cheapness  of  cast  iron 
over  steel,  however,  counteracts  these  factors  of  higher  cost. 
Where  the  rolls  must  be  very  strong  and  yet  not  too  large  in 
diameter,  and  for  sharp  corners,  which  would  crumble  if  made  of 
cast  iron,  steel  rolls  are  often  used.  The  steel  employed  should 
be  high  in  carbon,  —  say  0.50  to  0.75  per  cent. ;  but  any  case- 
hardening  of  steel  is  useless  here,  because  the  heating  of  the  rolls 


202 


THE  METALLURGY  OF   IRON  AND   STEEL 


by  the  material  passing  through  will  soon  draw  their  temper. 
This  heating  cannot  be  prevented  altogether,  though  it  is  custom- 
ary to  have  a  stream  of  water  flowing  over  the  rolls.  Sometimes 
nickel-steel  rolls  are  used  for  strength.  An  analysis  of  roll  metal 
of  a  very  large  American  company  is:  0.40  to  0-50  per  cent,  car- 
bon, 0.65  per  cent,  manganese,  3.25  per  cent,  nickel,  and  0.15  to 
0.20  per  cent.  siLcon. 

Diameter  of  Rolls.  —  With  smaller  rolls,  the  amount  of  power 
consumed  is  less  because  the  area  of  metal  under  vertical  pressure 


A  AND  C  =  OPEN  PASSES. 
B  =  CLOSED   PASS. 


C  =  DIAMOND  PASS. 


FIG.  139. 


is  less.  There  is  a  limit  below  which  the  diameter  cannot  go, 
however,  either  because  the  rolls  will  not  be  strong  enough  to  give 
the  desired  pressure,  or  they  will  not  grip  the  bar.  In  order  to  be 
gripped  the  upper  and  lower  edge  of  a  piece  must  touch  the  rolls 
at  a  point  not  more  than  30°  from  the  center  line  of  the  two  rolls 
(see  Fig.  140).  Every  effort  is  made  to  use  smaller  rolls,  because 
the  size  of  all  the  mills  is  regulated  by  them.  The  surfaces  of  all 
but  the  finishing-mill  are  usually  'ragged7  (i.e.,  made  rough),  to 
make  the  rolls  give  a  better  grip.  Those  to  receive  the  ingots 
are  ragged  the  most,  with  deep  indentations  somewhat  like  the 
of  cog-wheels,  whence  the  name  of  '  cogging  rolls'  for  this 


THE   MECHANICAL  TREATMENT   OF   STEEL 


203 


mill.1  The  next  trains,  known  as  the  'roughing  rolls/  are  also 
deeply  marked,  but  even  then  the  piece  must  come  within  the  30° 
line,  or  time  is  lost  in  trying  to  make  them  bite  the  piece. 

Speed  of  Rolls.  —  The  more  work  the  rolls  do,  the  slower  must 
they  revolve,  because  the  piece  entering  the  train  gives  a  shock  to 
the  mechanism  that  is  depend- 
ent upon  the  power  exerted 
and  the  momentum  of  the  mov- 
ing parts.  Thus  the  larger  the 
pieces  treated  the  colder  they 
are,  and  the  larger  the  rolls  the 
slower  must  be  the  speed.  In 
America,  speeds  are  at  the  high 
limit.  Reversing  slab-mills  may 
do  the  work  at  20  or  30  r.p.m. ; 
three-high  blooming  rolls  may 
run  over  50  r.p.m.;  mills  for 
finishing  rails,  100  r.p.m.;  and 
rod  mills  from  550  to  1200  r.p.m. 

Making  of  Rolls.  —  Cast-iron 
or  steel  rolls  are  cast  in  ap- 
proximately the  desired  shape 
and  then  turned  accurately  in 
a  lathe,  being  fitted  exactly  to  a 
templet  when  completed.  After 

rolling  some  thousand  tons  of  material,  they  become  worn  and 
produce  too  large  a  size  of  finished  shapes.  They  may  then  be 
used  for  a  larger  size  of  the  same  kind  of  article  by  putting  them 
back  in  the  lathe  and  turning  to  another  templet.  For  example, 
a  roll  for  a  20-inch  I-beam,  with  a  certain  thickness  and  width  of 
flange,  may  be  converted  to  one  for  a  20-inch  I-beam  with  thicker 
web  and  longer  flange. 

The  Mill.  —  The  different  parts  of  a  rolling-mill  may  be  seen  in 
Fig.  142.  The  wobblers  are  made  of  the  same  cross-section  as  the 
spindle,  some  examples  being  shown  ir.  Fig.  143.  The  coupling- 

1  In  America,  the  train  that  produces  blooms  (i.e.,  pieces  of  steel  usually 
about  6  to  8J  in.  square)  from  ingots,  is  sometimes,  but  not  always,  known  as 
'bloom  rolls/  or  'blooming  rolls/  instead  of  cogging  rolls;  and  the  train  that 
produces  'slabs'  (i.e.,  thick,  wide,  rectangular  pieces  that  are  to  be  rolled 
into  plates)  from  ingots  is  known  as  the  '  slabbing-mill.' 


FIG.   140. 


FIG.    141.  —  INDENTATIONS    ON   A   COGGING    MILL. 


FIG.    142. 

B,  Coupling  boxes;  C,  collars;  EEE,  roller  table  engine;  F,  fingers,  or  horns  on  manipulator; 
H,  housings;  HC,  housing  cap;  M,  manipulator  or  'Go-devil';  R,  roll;  S,  spindle;  T, 
roll  table;  TR,  table  rollers. 
204 


THE   MECHANICAL  TREATMENT   OF   STEEL 


205 


boxes  fit  over  the  spindle  and  wobblers,  so  that  neither  can  turn 
without  the  other.  In  some  mills  the  coupling-boxes  are  made 
of  cast  iron  in  order  that,  if  any  shock  comes  upon  the  driving 
mechanism,  the  boxes  shall  give  way  and  relieve  the  strain.  In 
other  mills  the  boxes  are  made  of  cast  steel,  as  it  is  thought  that  the 
constant  delays  due  to  broken  couplings  are  more  costly  than 
breakages  in  other  parts  of  the  mill.  The  spindles  are  at  least 


FIG.    143. 

B,  coupling  boxes;  C,  collars;  E,  roll  engine;  G,  guides;  H.  housings;  S,  spindles;  TR,  table 
roller;  HC,  housing  cap;  W,  wobblers;  TM,  table  motor. 

twice  as  long  as  the  coupling-boxes,  in  order  that  they  may  carry 
both  of  them  at  once  when  the  train  is  uncoupled.  Both  boxes 
slip  back  upon  the  spindle. 

Pinions  are  now  usually  made  of  steel  for  the  sake  of  strength. 
Housings  are  made  of  either  steel  or  of  cast  iron,  depending  on  the 
strains  to  which  they  are  subjected  and  the  opinion  of  the  manager. 
In  America,  they  are  usually  made  so  that  the  top  can  be  removed 
and  the  whole  train  of  rolls  removed  at  once,  together  with  the 
chocks,  and  several  mills  have  spare  sets  of  rolls  all  made  up  ready 


206 


THE  METALLURGY  OF   IRON  AND   STEEL 


and  carried  in  a  sling,  so  that  a  new  set  may  be  dropped  into  place 
with  a  crane  with  the  least  possible  delay  to  the  mill.  Delays  in 
rolling-mills  are  very  costly,  because  of  the  idle  labor  and  capital, 
and  because  other  parts  of  the  plant  may  be  delayed  thereby. 


FIG.    144. —  A   PINION. 
W  =  wobbler. 

The  screw-down  mechanism  which  adjusts  the  distance*  be- 
tween the  rolls  is  operated  usually  by  hydraulic  pressure,  though 

electric  motors  are  coming  into 
vogue.  It  is  connected  with  a 
telltale  gage  which  advises  the 
roller  exactly  as  to  the  distance 
separating  the  rolls. 

Guards  are  of  steel  and  serve 
to  peel  the  piece  off  the  roll  and 
prevent  it  encircling  the  roll 
(called  t  collaring')  in  case  it  be- 
comes wedged  between  the  col- 
lars. They  must  be  upon  the 
lower  roll,  as  shown  in  Fig.  145, 
or  upon  the  upper  roll,  and  coun- 
terbalanced to  hold  them  in  posi- 
tion, when  they  are  called  '  hang- 
ing guards.'  Guides  are  on  the  opposite  side  of  the  train,  and  assist 
in  conducting  the  piece  straight  into  the  groove. 

Roll  Tables.  — Heavy  pieces  are  handled  at  the  rolls  by  sup- 
porting them  upon  a  series  of  rollers,  situated  in  front  of  and  behind 
the  roll  train,  and  known  as  the  'tables/  At  two-high  mills  the 
tables  are  stationary ;  at  three-high  mills  the  front  and  back  tables 


FIG.    145. 


THE   MECHANICAL  TREATMENT  OF   STEEL 


207 


are  sometimes  raised  and  lowered  together  by  hydraulic  or  elec- 
tric mechanism,  and  sometimes  they  are  pivoted  near  the  middle, 


FIG.    146. 

A,  hanging  guards;  B,  coupling  boxes,;  H,  housings;  P,  pinions;  PH,  pinion  housing;  R, 

rolls;  S,  spindles. 

so  that  the  end  next  the  rolls  can  be  tilted  upward  in  order  to 
bring  the  piece  between  the  guides  which  direct  it  into  the  groove. 


FIG.    147. 
G,  guides;  HC,  housing  cap;  PH,  pinion  housing;  RR,  rolls. 

The  rollers  to  handle  large  pieces  are  'live/  that  is,  they  are  made 
to  revolve  by  electric  motors  and  thus  move  the  piece  back  and 


FIG.    148. 
D.  Screw-down  mechanism;  EEE,  table  engine;  TM,  table  motor;  TR,  table  roller. 


__ 


FIG.    149.  —  TWO-HIGH,   REVERSING  UNIVERSAL   MILL. 

VVV,  Vertical  rolls;  RR,  Horizontal  rolls. 
208 


OQ    H 


210  THE  METALLURGY   OF   IRON   AND   STEEL 

forth.  'Dead'  rollers  are  used  where  pieces  are  to  be  moved  by 
hand. 

Transfer  Tables.  —  Roller  tables  are  sometimes  made  so  that 
they  may  be  moved  bodily  from  one  roll  train  to  another,  carrying 
the  piece  of  metal  with  them,  and  so  connected  electrically  that  the 
rollers  can  be  caused  to  revolve  when  the  table  is  in  any  location. 

Manipulators.  —  If  two  or  more  posts,  supported  on  a  carriage 
which  can  be  moved  laterally,  project  between  the  rollers  of  a 
table,  their  sidewise  motion  will  transfer  the  piece  from  one  pass 
to  another.  If  the  table  is  of  the  lifting  type,  the  posts,  or  'horns,' 
or  '  fingers'  can  be  brought  to  such  a  position  that  the  lowering  of 
the  table  will  bring  the  edge  of  the  piece  upon  the  horns  and  thus 


FIG.    151. 

tip  it  on  to  the  other  side.  This  form  of  manipulator  is  much  used 
at  three-high  blooming  rolls,  and  is  very  efficient  and  rapid  in  its 
work.  The  same  type  is  used  at  reversing  blooming  rolls,  but  the 
pie<?e  is  more  usually  tipped  over  by  the  roller  with  the  tool  shown 
in  Fig.  151. 

Roll  Engines.  —  The  service  on  rolling-mill  engines  is  very 
severe,  because  the  full  load  comes  upon  it  when  the  piece  enters  the 
rolls,  and  then  leaves  it  as  suddenly  again.  To  equalize  these 
sudden  variations  of  power,  all  but  the  reversing  engines  are  built 
with  very  large  and  heavy  fly-wheels  and  run  at  a  high  rate  of 
speed  (from  30 'to  250  r.p.m.),  with  governors  of  a  quick-acting 
type.  The  Allen  engine  with  the  Porter  governor  serves  these 
purposes,  and  the  Porter- Allen  type  is  much  used.  The  ordinary 
slide-valve  is  used  on  the  smaller  engines.  Corliss  valves  are  com- 
moner in  America  for  engines  doing  heavy  work  (1000  to  3500  H.P.) , 
while  piston-valves  are  favored  in  England.  The  fly-wheel  is 
placed  upon  the  crank-shaft,  to  which  the  roll  train  is  directly 


212 


THE   METALLURGY   OF    IRON   AND   STEEL 


coupled.     The  fly-wheels  very  exceptionally  weigh  as  much  as  75 
and  100  tons  or  more. 

Piston-valves  are  used  almost  always  for  reversing  engines 
which  are  compounded,  so  they  may  never  come  to  rest  at  a  dead 


FIG.    153.  —  UNIVERSAL   MILL. 

E,  Engine  for  horizontal  rolls;  EE,  engine  for  vertical  rolls;  EEE,  roller  table  engine; 
TT,  roll  tables;  TR,  TR,  table  rollers. 

point.  There  is,  of  course,  no  fly-wheel,  and  the  engine  is  directly 
coupled  from  the  crank-shaft  to  the  roll  train  in  the  large  American 
mills,  but  is  geared  down  so  that  the  engine  can  develop  a  higher 


FIG.    154.  —  MOTOR-DRIVEN    ROLLING   MILL. 

speed  than  is  desired  for  the  rolls,  thus  requiring  less  power. 
Reversing  slabbing-mill  engines  have  capacities  up  to  25,000  H.P. 
each. 


THE  MECHANICAL  TREATMENT  OF  STEEL 


213 


Electric- Motor  Drive.  —  During  the  year  1906,  very  important 
installations  were  made  of  electric-motor-driven  roll  trains.  The  ad- 
vantages of  electricity  over  steam  are  a  lower  operative  cost,  greater 


security  of  operation,  fewer  breakdowns,  and  a  more  flexible  rela- 
tion between  the  prime  mover  and  the  load,  the  result  of  electric 
motors  receiving  a  sudden  shock  more  elastically.  On  the  other 
hand,  the  advantage  of  steam  is  that,  although  it  receives  the 
load  less  elastically,  it  adjusts  itself  quicker  and  better  to  the  ex- 


214 


THE   METALLURGY   OF    IRON   AND   STEEL 


treme  variations  in  load  that  always  occur  in  rolling-mills.     This 
is  especially  true  of  reversing  mills. 

As  already  noted,  the  smaller  the  mill  the  less  will  be  the  load, 
and  therefore  the  variation  in  load.     Consequently,  in  England, 


Sweden  and  Germany  there  are  many  motor-driven  roll  trains  of 
the  smaller  size,  and  a  few  up  to  several  hundred  horse-power,  in- 
cluding one  reversing  motor  of  1200  H.P.  In  America,  there  are 
some  small  roll  trains  operated  by  electricity,  but  up  to  1906  there 


THE   MECHANICAL  TREATMENT   OF   STEEL  215 

was  only  one  with  as  high  a  capacity  as  1500  H.P.  During  1906, 
at  some  of  the  most  important  works  in  the  country,  motor-driven 
rail  mills  were  begun,  including  two  motors  of  1500  H.P.  each  for  a 
three-high  train,  and  also  including  a  rail  mill  operated  throughout 
by  electricity,  from  the  bloom  rolls  to  the  finishing  train,  with  six 
motors,  varying  in  capacity  from  2250  H.P.  to  6000  H.P.  each. 
The  most  startling  innovation,  however,  is  a  reversing  Universal 
plate-mill  operated  by  two  motors  on  the  same  shaft,  which,  when 
running  at  full  speed  (150  r.p.m.),  will  develop  approximately 
10,000  H.P.  It  is  supposed  that  this  mill,  when  built,  will  be 
capable  of  reversing  from  full  speed  forward  to  full  speed  backward 
in  the  space  of  three  seconds. 

Almost  all  American  rolling-mills  of  most  modern  equipment 
now  use  electric  power  for  driving  the  table  rollers,  the  screw- 
down  mechanism,  the  shears,  and  in  fact  for  all  purposes  except 
driving  the  rolls. 

ROLLING-MILL  PRACTICE 

Troubles  in  Rolling.  —  There  are  more  difficulties  met  with  in 
rolling-mill  practice  than  we  can  discuss  here,  but  it  may  be  said 
that  the  seriousness  of  a  difficulty  is  estimated  almost  altogether 
in  proportion  to  the  delay  it  causes  in  the  operation  of  the  mill, 
rather  than  in  the  loss  of  a  small  amount  of  material  or  of  a  part 
of  the  mill  itself.  For  example,  the. breaking  of  a  table  engine, 
roller,  or  even  a  roll,  is  regretted  more  because  of  the  time  necessary 
to  put  in  a  new  one  than  because  of  the  loss  of  the  part.  This  is 
one  reason  why  electric  motors  to  operate  the  tables  have,  in  many 
cases,  replaced  small  steam  engines.  The  same  conditions  have  also 
resulted  in  different  parts  of  the  mill  being  made  interchangeable. 
In  many  mills  it  is  customary  to  have  spare  table 
engines  or  motors,  etc.,  always  ready,  and  the  least 
accident  to  one  of  these  machines  would  result  in  its 
being  immediately  replaced  by  a  whole  new  one. 

The  most  important  common  troubles  in  rolling- 
mill  operations,  probably,  are:  (1)  Bending  and 
breaking  of  the  rolls,  due  to  their  being  placed  under  too  severe  a 
strain,  either  because  the  draft  is  too  heavy  or  because  the  piece  is 
cooled  too  much ;  (2)  the  fins  caused  by  metal  being  squeezed  out  be- 
tween the  collars  of  the  rolls,  as  shown  in  Fig.  157 ;  these  fins,  besides 
spoiling  the  material,  are  liable  to  break  the  rolls;  (3)  collaring. 


FIG.    159.  —  UNIVERSAL   MILL. 


FIG.    160.  —  THREE-HIGH   PLATE   MILL. 


216 


THE   MECHANICAL  TREATMENT  OF   STEEL 


217 


Rolling  Plates.  —  In  the  rolling  of  plates  an  ingot,  usually  of 
open-hearth  steel  and  weighing  2  to  10  tons,  is  first  cogged  down 
in  the  slabbing-mill,  producing  a  long,  flat  piece  of  metal.  The 
slabbing-mills  are  frequently  of  the  two-high,  reversing,  Universal 


FIG.  161.  —  THREE-HIGH  PLATE  MILL,  TWO  STANDS  OF  ROLLS. 

B,  Coupling  boxes;  D,  screw-down  mechanism;  E,  roll  engine;  H,  housings;  P,  pinions; 
PH,  pinion  housing;  RR,  rolls;  S,  spindles. 

type.  The  front  end  of  the  piece  is  cut  off  in  a  huge  hydraulic  or 
electric  shear  to  remove  the  pipe  and  then  it  is  cut  up  into  slabs 
of  the  desired  size  or  into  slabs  of  a  size  such  that  each  one  will  make 
one  plate.  The  slabs  are  then  transferred  to  the  heating  furnace, 
heated  to  about  1300°  C.,  and  rolled  in  a  three-high  or,  more  rarely, 


FIG.    162.  — OTHER   VIEW   OF   FIG.    161,    SHOWING    METHOD    OF    RAISING 
THE   ENDS   OF   THE   TABLES   NEXT   TO   THE   ROLLS. 

a  two-high  reversing  plate-mill,  in  some  cases  there  being  a  pair  of 
vertical  rolls  to  keep  the  edges  straight.  During  the  rolling  a 
shovelful  of  salt  is  occasionally  thrown  upon  the  surface  of  the 
plate,  which  carries  in  between  the  rolls  some  of  the  water  which 
is  always  trickling  over  them  to  keep  them  cool.  Sand  may  be 


FIG.    163. —  PLATE   STRAIGHTENING   ROLLS. 


218 


FIG.    164. —  PLATE   SHEARS. 


THE   MECHANICAL  TREATMENT  OF   STEEL 


219 


used  for  the  same  purpose,  and  in  England  heather  is  sometimes 
used.  As  soon  as  this  water  is  pressed  against  the  hot  plate  it  is 
converted  into  steam,  causing  a  rapid  series  of  explosions  which 
blow  the  scale  off  the  upper  surface  of  the  plate  and  give  it  a 
smoother  finish.  As  the  process  continues,  the  operator  tests  the 
thickness  of  the  plate  with  a  gage,  and  when  it  is  of  the  desired 
thickness,  it  is  passed  up  to  the  straightening  rolls  and  then  to  a 


-flH 


12 


FIG.    165. 

cooling  table,  being  marked  with  a  distinguishing  mark  on  the  way 
to  indicate  the  heat  of  steel  from  which  it  was  manufactured. 
When  cooled  it  is  sheared  to  the  desired  size  and  shape.  The  weight 
of  finished  plate  will  probably  be  not  more  than  80  per  cent,  of 
the  weight  of  the  steel  sent  to  the  rolling-mill  in  the  form  of  ingots. 
Rolling  Rails.  —  An  ingot  of  about  three  tons  in  weight  is  sent 
to  the  rolling-mill,  where  it  is  kept  in  the  heating  furnace  for  50 
minutes  or  more  until  the  interior  is  entirely  solid  and  it  is  of  a  uni- 
form temperature  throughout.  It  is  then  rolled  into  blooms, 
either  in  a  three-high  mill,  such  as  shown  in  Fig.  142,  or  in  a  two- 


220 


THE  METALLURGY  OF   IRON  AND   STEEL 


high  reversing  mill.  In  the  three-high  mill,  an  ingot  18J  in.  square 
at  the  middle  (tapering  about  J  to  j  inch  to  a  foot  in  order  that 
the  mold  may  be  more  easily  removed)  will  be  reduced  to  a  bloom 
of  about  8  in.  square  in  nine  passes,  the  amount  of  reduction  in  each 
pass  being  about  12  to  18  per  cent,  of  the  original  area.  The  top 
end  is  then  cut  off  to  remove  the  pipe,  the  bottom  end  to  remove 
the  irregularity  due  to  the  rolling,  and  the  piece  cut  in  two  to  make 
two  blooms.  The  blooms  are  then  generally  reheated  in  a  heating 
furnace  and  passed  through  the  series  of  changes  shown  in  Fig.  165, 
until  they  have  assumed  the  proper  size  and  form,  the  greatest 


FIG.    166. 

amount  of  draft  being  usually  not  more  than  22  per  cent.,  except 
upon  the  middle  portion  of  the  web.  In  some  cases  the  blooms 
are  not  reheated,  but  go  directly  from  the  bloom  rolls  to  the  first 
roughing  train.  This  makes  the  metal  crack  more  in  rolling,  how- 
ever, and  these  cracks  will  ultimately  show  as  a  mark  on  the  fin- 
ished product,  which  causes  the  rails  to  be  classified  by  the  in- 
spector in  the  second  or  third  class.  Railroads  will  accept  only 
5  or  10  per  cent,  of  their  order  in  second-class  rails,  while  third- 
class  rails  are  not  acceptable  and  must  go  into  the  tracks  of  the  steel 
company  itself  or  else  be  reheated  and  rolled  into  smaller  sizes, 
whereby  the  marks  will  often  be  eliminated.  If  the  blooms  are 
reheated  before  going  to  the  roughing  train,  many  of  the  cracks 


THE  MECHANICAL  TREATMENT  OF   STEEL 


221 


formed  during  blooming  will  be  seemingly  closed  up,  or  in  any 
event  will  not  show.  Furthermore,  if  this  reheating  is  to  take 
place,  the  ingots  need  not  be  heated  so  hot  in  the  first  instance, 
and  therefore  will  not  be  so  tender  and  so  liable  to  crack. 


Making  Lap-Welded  Tubing.  —  The  wrought  iron  or  steel  low 
in  carbon  is  first  rolled  out  into  skelp  about  20  to  25  ft.  long,  and 
of  a  width  a  little  more  than  three  times  the  intended  diameter  of 
the  tube.  The  skelp  is  then  rolled  up  into  a  rough  form  of  a  pipe, 


222 


THE  METALLURGY  OF   IRON   AND   STEEL 


as  shown  in  Fig.  168,  by  passing  it  sidewise  through  rolls,  which 
bend  it  roughly  to  the  shape  of  a  pipe,  with  edges  overlapping. 
The  same  is  done  in  the  case  of  small  2-to-8-in.  tubes,  by  draw- 
ing them  through  a  die.     It  is 
then  passed  at  a  welding  heat 
through  a  pair  of  rolls,  with 
the  seam  that  is  to  be  welded 


FIG.    168. 


FIG.    169.  —  MANDRIL. 


upward.  Between  the  rolls  is  a  mandril,  on  the  end  of  a  long 
rod  and  of  the  size  of  the  inner  diameter  of  the  tube.  The  rolls 
press  the  two  parts  of  the  weld  together  over  the  mandril,  and  the 
pipe,  after  another  rolling  to  give  true  size  and  after  straightening 
and  testing,  is  ready  for  service. 

Making  Seamless   Tubes.  —  Seamless   or   weldless   tubes   are 
made  either  by  distorting  a  steel  plate  between  dies,  as  shown  in 


FIG.    170.  —  PIPE-WELDING  ROLLS. 


Fig.  172,  or  else  by  piercing  a  hole  through  the  center  of  a  hot  steel 
billet  and  then  rolling  it  successively  between  rolls  over  a  mandril. 
The  hole  is  sometimes  first  of  small  size  and  then  expanded  by 
pressing  larger  and  larger  expanders  through  it.  The  pierced 


FIG.    171.  —  PIPE-WELDING    ROLLS   WITH    MANDRIL    IN   POSITION. 
1 


FIG.    172. 


223 


224  THE  METALLURGY  OF  IRON  AND  STEEL 

billet  is  then  rolled  over  mandrils  constantly  decreasing  in  size 
until  the  inner  and  outer  diameters  are  brought  to  the  desired  size. 
Butt-Welded  Tubes.  —  Butt-welded  tubes  are  made  by  heating 
the  skelp  to  a  welding  temperature  and  then  drawing  it  out  of  the 
furnace  through  a  bell,  as  shown  in  Fig.  173,  which 
curls  it  up  and  welds  the  edges  together,  with- 
out lapping.   Butt-welded  tubes  are  not  so  strong 
as  lap- welded  tubes,  and  are  not  usually  used  for 
boilers  or  high  pressures,  or  where  they  will  be 
expanded  much  by  heat  during  service.     They 
are  mostly  made  in  the  small  sizes. 

In  the  United  States,  over  a  million  and  a 
half  tons  of  pipe  are  made  each  year.  It  is  used 
principally  for  the  transmission  of  oil,  water, 
steam  and  gas,  and  for  conduits  for  electric  wires.  About  30 
per  cent,  of  this  is  made  of  wrought,  and  70  per  cent,  of  soft 
weld-steel.  The  steel  is  usually,  but  not  always,  made  by  the 
Bessemer  process  on  account  of  the  difficulty  of  making  very  low- 
carbon  material  in  the  open-hearth. 

WIRE  DRAWING 

Wire  is  a  product  formed  by  being  drawn  cold  through  a  die. 
The  commonest  shapes  are  'rounds/  and  the  next,  hollow  tubes, 
but  a  great  variety  of  forms  may  be  produced  at  will. 

Effect  of  Drawing.  —  The  effect  of  the  drawing  is  to  produce  a 
very  exact  size  of  material  and  to  increase  the  strength,  hardness, 
and  brittleness  of  the  metal.  In  the  drawing  of  steel,  the  crystals 
of  the  metal  are  actually  pulled  apart  and  flow  by  each  other,  the 
outer  layers  of  the  metal  being  dragged  back  over  the  central  core, 
there  being  at  the  same  time  a  pressure  exerted  in  all  directions 
toward  the  center,  which  results  in  a  certain  amount  of  backward 
flowing  even  there.  Because  the  crystals  are  so  broken  up  during 
the  operation,  and  because  the  metal  is  never  heated  above  its 
critical  temperature  during  annealing,  the  grain  of  the  steel  is  very 
fine  and  the  crystals  are  intimately  mixed,  which  is  probably  the 
cause  of  the  great  strength  of  wire. 

Annealing.  —  With  each  draft  the  wire  becomes  harder  and 
more  difficult  to  draw.  As  it  is  pulled  through  the  die  by  a 
force  equal  to  40  to  80  per  cent,  of  its  tensile  strength,  it  is  neces- 


THE   MECHANICAL  TREATMENT   OF   STEEL 


225 


sary  to  soften  it  at  intervals  by  annealing,  iest  it  break.     The  an- 
nealing is  accomplished  by  enclosing  the  wire  in  some  receptacle 


FIG.    174. —  WIRE    ROD    ROLLING   TRAIN. 
These  mills  will  roll  steel  down  to  from  J  to  ^  inch  rods,  which  are  then  drawn  into  wire. 

that  protects  it  from  oxidation  and  then  heating  to  a  low-red  heat. 
In  the  case  of  steel,  it  is  required  after  every  8  to  3  passes,  de- 


FIG.    175. —  WIRE   ROD   FRAME. 

pending  upon  the  amount  of  carbon  in  the  metal  and  the  amount 
of  draft. 


226 


THE  METALLURGY  OF   IRON   AND   STEEL 


Dies.  —  Wire  dies  are  usually  made  of  high-carbon  steel  (say 
about  2  per  cent.),  through  which  a  tapered  hole  is  made,  as  shown 
in  Fig.  176.  The  object  of  using  this  material  is  that,  as  it  becomes 
worn  in  service,  it  can  be  reformed  and  used  for  larger  sizes,  which 
could  not  be  done  with  white  cast  iron. 

Bench.  —  A  '  bench '  on  which  wire  is  drawn  consists  of  a 
reel  which  holds  the  coil  of  undrawn  wire,  a  die  support,  and  a 
second  reel  which  draws  the  wire  through  the  die  and  coils  it  up, 

and  which  is  driven  by  bevel  gears. 
The  die  rests  against  the  support,  and 
the  wire,  having  a  tapered  point,  is 
thrust  through  the  hole  and  grasped 
by  a  pair  of  tongs,  which  pulls  it  out 
until  it  can  be  attached  to  the  reel. 
This  is  then  set  in  motion  and  draws 
the  wire  through.  The  die-holder  is 
heaped  up  with  lubricant  of  some  kind, 
in  order  that  the  metal  may  pass  more 
easily  through  the  hole.  The  speed  at 
which  wire  is  drawn  will  vary  from 
75  to  750  feet  per  minute,  depending 
upon  the  size  and  hardness  of  the 
material  drawn  and  the  amount  of 

reduction  during  each  draft.  In  many  cases  there  is  more  than 
one  die,  and  the  wire  passes  successively  through  two,  three  or 
more,  being  constantly  reduced  in  each  one.  Between  each  pair 
of  dies  is  a  reel,  around  which  the  wire  passes  two  or  three  times, 
since  the  strength  of  the  wire  emerging  from  the  last  die  would 
not  be  sufficient  to  draw  it  through  all  of  the  holes. 

Draft.  —  The.  heavier  the  draft  the  greater  is  the  hardness 
produced  in  the  wire  and  the  greater  the  wear  of  the  dies.  The 
average  amount  of  draft  will  probably  be  from  20  to  25  per  cent. 
Drawing  Tubes.  —  Hollow  wire  or  small  tubes  are  drawn 
sometimes  over  a  mandril.  This  mandril  may  be  a  wire  of  about 
the  size  of  the  inner  diameter  of  the  finished  tube.  After  several 
drafts,  the  tube  is  wedged  so  tightly  on  the  mandril  that  it  cannot 
be  separated.  It  is  then  given  an  unbalanced  squeeze  between  a 
pair  of  rolls,  so  that  the  tube  is  reduced  in  thickness,  whereby  its 
diameter  is  increased  and  the  mandril  may  easily  be  withdrawn. 


FIG.  176.  —  SECTION  OF 
WIRE  DIE. 


THE   MECHANICAL  TREATMENT  OF   STEEL 
PRESSING 


227 


Steel  may  be  pressed  either  hot  or  cold,  the  latter  method 
being  used  chiefly  for  thin  and  soft  steel,  and  the  former  for  very 
large  work,  such  as  armor-plate,  cannon,  etc.,  for  which  hydraulic 
presses  have  now  largely  replaced  the  heaviest  steam-hammers. 


FIG.    177.  —  FOURTEEN-THOUSAND-TON    ARMOR-PLATE   PRESS. 

Effect  of  Pressing.  —  The  effect  of  pressing  upon  the  metal  is 
almost  exactly  the  same  as  that  of  hammering,  except  that  its 
action  extends  a  little  deeper  into  the  material,  thus  giving  a 
somewhat  superior  texture  to  this  part  of  the  body.  Tests  cut 


228  THE  METALLURGY  OF   IRON   AND   STEEL 

from  the  center  of  large  pieces  forged  under  the  press  are  very 
much  superior  to  those  cut  from  the  same  place  in  pieces  forged 
under  the  hammer. 

Hot-Pressing.  —  Presses  vary  in  size  usually  from  600  to 
14,000  tons.  They  may  be  either  of  the  continuous  or  of  the 
intermittent  type.  In  the  latter,  the  amount  of  pressure  exerted 
increases  step  by  step  as  the  work  progresses.  The  amount  of 
work  that  can  be  done  by  the  press  in  large-sized  pieces  is  greater 


FIG.   178.  —  DROP-FORGING  PRESS  FOR   PLATES. 

than  that  done  by  hammers  for  the  same  amount  of  power  used. 
This  results  in  a  double  saving  of  fuel,  since  more  work  can  be 
accomplished  with  one  heating.  By  means  of  the  10,000-ton 
press  at  the  Homestead  Steel  Works,  a  50-ton  armor-plate  has 
been  reduced  2  in.  in  thickness  and  moved  forward  6  in.  for  each 
squeeze,  while  a  3000-ton  press  at  the  Firths  Works  in  England 
has  reduced  a  30-ton  ingot  from  49  to  28  in.  diameter  in  30  minutes, 
and  from  51  to  26  in.  diameter  in  65  minutes.  Small  pieces  can 
be  turned  out  a  little  faster  under  the  hammer. 

Cold-Pressing.  —  Thin  plate  for  steel  railroad-car  construction 
is  often  formed  by  pressing  it  cold  between  dies  under  hydraulic 
presses  of  from  30-  to  800-tons  capacity.  In  this  way  bolsters, 
braces,  and  many  other  parts  are  formed  with  great  economy. 
Sometimes  two  or  three  presses  are  required  with  different  dies  to 
complete  the  shaping,  and  occasionally  it  is  necessary  to  press  some 
of  the  work  hot,  because  the  distortion  is  so  great  that  the  steel 


THE  MECHANICAL  TREATMENT  OF   STEEL  229 

would  otherwise  be  torn.  .Cold-pressing  is  also  known  as '  flanging/ 
It  has  one  great  difference  from  hot-pressing,  in  that  there  is  no  re- 
duction in  the  sizes  of  pieces  treated. 

COMPARISON  OF  MECHANICAL  METHODS 

Hot-Rolling  with  Cold-Rolling.  —  Cold-rolling  gives  a  harder 
material  and  more  accurate  finish  as  to  size  than  any  form  of 
hot- working.  Furthermore,  it  produces  a  finer  grain  in  the  metal. 
If  the  cold-rolling  is  followed  by  annealing  at  a  temperature  below 
the  critical  range  of  the  steel  (see  pages  388  to  389),  the  material 
retains  its  fine  grain,  and  is  stronger  and  more  ductile  than  metal 
that  has  been  worked  hot.  Before  cold-rolling,  the  metal  is 
pickeled  in  dilute  sulphuric  acid  to  remove  the  scale,  and  is  there- 
fore produced  with  a  bright  surface  which  is  suitable,  without 
machining,  for  use  as  shafting,  for  nickel-plating,  etc.  The 
annealing  is  usually  effected  inside  closed  vessels,  in  a  reducing 
atmosphere  of  illuminating  gas  or  some  similar  medium,  which 
prevents  the  formation  of  scale.  Cold-rolled  steel  is  used  for 
articles  that  are  to  be  drawn  or  stamped  to  shape  —  watch  and 
clock  springs,  hacksaw  blades,  corset  steels,  etc. 

Hammering  versus  Rolling  and  Pressing. — Of  all  the  mechanical 
methods,  rolling  gives  by  far  the  largest  output  per  day,  per  unit 
of  power,  and  usually  per  unit  of  fuel  for  heating.  It  is  therefore 
the  cheapest  method,  especially  for  labor.  It  does  not  work  the 
metal  as  well  as  either  hammering  or  pressing,  both  of  which  pro- 
duce a  much  better  crystalline  structure,  beside  affording  a  better 
control  of  the  temperature  at  which  the  operation  is  ended. 
Pressing  works  the  metal  at  greater  depths  than  hammering,  and 
is  therefore  especially  advantageous  for  producing  large  pieces, 
and  the  more  so  because  small  presses  are  very  costly  to  install  as 
compared  to  steam-hammers.  Where  a  shape  is  intricate,  rolling 
is  more  liable  to  tear  the  metal  than  hammering  or  pressing  be- 
cause, at  the  point  where  the  roll  is  deeply  cut,  its  surface  velocity 
is  much  less  than  where  the  diameter  is  greater,  and  thus  it  tends 
to  drag  the  metal  through  at  different  speeds. 

HEATING  FURNACES 

Heating  furnaces  are  usually  of  the  reverberatory  type,  burn- 
ing soft  coal  or  gas.  The  flame  produced  must  be  as  reducing  as 


THE   MECHANICAL  TREATMENT  OF   STEEL  231 

possible  in  order  to  produce  a  small  amount  of  scale.  Much  better 
control  is  obtained  if  the  ash-pit  is  enclosed  and  forced  draft  is 
used  to  burn  the  fuel.  In  this  way  about  half  a  ton  of  fuel  will  be 
required  to  heat  a  ton  of  steel  from  the  atmospheric  temperature 
to  that  necessary  for  mechanical  work,  with  a  loss  of  about  4  to  5 
per  cent,  of  the  metal  as  scale.  The  gases  must  necessarily  leave 
the  furnace  at  a  high  temperature,  and  therefore  it  is  not  uncom- 
mon to  have  boilers  situated  over  the  heating  furnace,  in  which 
steam  is  raised  by  means  of  the  waste  heat.  With  this  economy 
the  amount  of  fuel  chargeable  against  heating  the  steel  will  be 
from  350  to  450  pounds  per  short  ton  of  steel  heated. 

Regenerative  Furnace.  —  If  the  heating  furnaces  are  fired  with 
producer  gas  and  the  regenerative  method  is  employed,  we  get  a 
far  better  control  of  the  temperature  and  of  the  reducing  influence 
of  the  furnace  gases.  By  this  means  a  short  ton  of  steel  may  be 
heated  with  from  150  to  200  pounds  of  fuel  and  with  a  loss  of 
metal  of  from  1  to  5  per  cent,  by  oxidation. 

Continuous  Furnaces.  —  Billets  and  other  small  pieces  may  be 
heated  in  furnaces  whose  action  is  continuous.  Such  a  one  as 
this  is  shown  in  section  in  Fig.  180.  Along  the  hearth  stretch 
two  lines  of  pipe,  which  are  kept  cool  by  a  stream  of  water  inside. 
Upon  the  pipes  is  laid  a  long  series  of  billets,  which  are  gradually 
moved  forward  toward  the  end  at  which  the  gas  and  air  enter.  In 
this  way  the  flame  is  always  met  by  colder  material  and  finally 
leaves  the  furnace  at  a  relatively  low  temperature.  As  the  gases 
pass  out,  they  go  through  a  series  of  pipes,  B,  B,  around  which 
circulates  the  air  that  is  afterward  led  to  the  fire  and  used  for  com- 
bustion. As  soon  as  the  billet  nearest  the  fire  end  is  heated  to  the 
desired  temperature,  a  new  one  is  pushed  in  at  the  bottom,  caus- 
ing the  hot  billet  to  be  shoved  onto  the  inclined  plane,  whence  it 
rolls  out  of  the  furnace  to  the  point  A,  whence  it  is  transferred  to  the 
rolling-mill.  In  this  type  of  furnace  a  short  ton  of  steel  may  be 
heated  with  from  120  to  145  pounds  of  fuel,  with  a  loss  in  weight 
of  less  than  1  per  cent,  by  oxidation. 

Soaking-Pits.  —  Ingots  with  molten  interiors  must  be  put  in 
some  form  of  furnace  in  which  they  will  stand  upright  until  they 
have  solidified  throughout  and  are  ready  to  roll,  in  order  that  the 
pipe  may  form  in  the  upper  portion.  The  type  of  furnace  used 
for  this  is  known  as  a  soaking-pit  and  is  shown  in  Fig.  181. 
The  original  intention  of  soaking-pits  was  to  have  the  heat  in  the 


THE   MECHANICAL  TREATMENT   OF   STEEL 


233 


ingot  itself  bring  the  interior  of  the  furnace  and  the  mass  of  metal 
to  the  desired  temperature ;  but  this  is  not  found  practicable  in  the 
United  States,  and  soaking-pits  are  usually  heated  by  regenerated 
gas  and  air.  The  ingots  must  be  kept  in  these  soaking-pits  long 
enough  to  be  entirely  solid  in  the  interior,  and  for  this  purpose  at 


•rt-^+lv^v/:;.:^.^;;:^ 

FIG.    181.  — BRICKWORK   OF   REGENERATIVE   GAS   SOAKING-PIT. 

least  55  minutes  are  required  for  3-ton  ingots  when  stripped  and 
charged  as  soon  as  possible  after  teeming,  and  more  for  ones  of 
larger  size. 

Furnace  Bottoms.  —  Heating-furnace  bottoms  must  be  of  some 
material  not  readily  corroded  by  oxide  of  iron  scale,  and  basic  bot- 
toms are  very  commonly  employed  with  success.  Heating-fur- 
naces are  also  frequently  supplied  with  a  tap-hole,  from  which  the 
slag,  composed  chiefly  of  oxide  of  iron,  can  be  tapped  at  intervals. 
Soaking-pit  bottoms  are  frequently  covered  with  a  layer  of  coke 
breeze  to  absorb  the  slag  and  prevent  corrosion  of  the  furnace 
bottom.  This  is  shoveled  out  when  an  opportunity  is  afforded, 
and  new  breeze  substituted,  or  is  knocked  out  through  a  hole  in  the 
bottom,  for  which  see  Fig.  181. 

Heating  Practice.  —  In  heating  steel  for  rolling,  the  lower  the 
temperature  the  better  will  be  the  quality  of  the  product.  On 


234      THE  METALLURGY  OF  IRON  AND  STEEL 

the  other  hand,  if  the  metal  is  to  undergo  many  passes  before  it 
receives  another  heat,  it  must  be  correspondingly  hot,  in  order 
that  the  finishing  temperature  may  be  high  enough  to  avoid  ex- 
cessive power  for  reduction.  There  is  no  doubt  that  rolling  tem- 
peratures at  the  present  time  are  higher  than  they  should  be,  for 
the  metal  when  finished  should  be  only  just  above  the  critical 


FIG.    182.  —  CHARGING   A   SLAB   INTO   A   HEATING   FURNACE. 

temperature  of  the  steel.  Until  within  recent  years  no  suitable 
pyrometers  for  measuring  the  temperature  have  been  available, 
and  the  temperature  for  drawing  the  material  is  judged  by  eye,  so 
that  no  figures  can  be  given.  There  can  be  no  doubt  that  more 
careful  attention  to  this  point  will  result  in  less  waste  in  rolling 
(on  account  of  the  production  of  cracked  or  second-class  material 
because  of  too  hot  steel  at  the  starting)  and  in  the  production  of 
a  higher  quality  of  steel. 

It  must  be  remembered,  however,  that  the  steel  must  be  hot 
enough  to  cause  it  to  weld  together  wherever  it  has  become  cracked. 
'This  is  especially  to  be  observed  in  low-carbon  steel  whose  welding, 
as  well  as  its  melting-point,  is  higher  than  that  of  high-carbon  steel. 


THE   MECHANICAL  TREATMENT   OF   STEEL  235 

The  casting  temperature  and  the  absence  of  ingotism  which  the 
author  has  discussed  elsewhere  is  probably  more  important  than 
any  other  factor  in  preventing  cracking  during  rolling,  as  properly 
made  steel  can  stand  without  injury  a  high  temperature  which 
would  be  very  harmful  otherwise.  High-carbon  steel  is  very 
delicate  to  roll  especially  when  the  silicon  is  also  high. 

REFERENCES  ON  MECHANICAL  TREATMENT 

See  especially  No.   31  and   the  current   technical   literature, 
especially  Nos.  8,  9  and  12. 


IX 
IRON  AND   STEEL   FOUNDING 

FOUNDING  is  a  mechanical  art,  and  consists  in  pouring  melted 
metal  into  a  mold  of  any  desired  size  and  form,  which  the  metal 
assumes  and  retains  when  cold.  The  mold  is  made  of  some  kind 
of  sand,  with  rare  exceptions  to  be  mentioned  hereafter.  The  art 
is  a  very  complex  one,  added  to  which  it  is  now  passing  through  an 
important  transition  period  in  which  science  is  very  rapidly  taking 


Sweeping  up  a  mold. 
FIG.    185. —  VIEW    IN   AN    IRON    FOUNDRY. 

the  place  of  rule  of  thumb.  It  is  impossible  to  treat  the  subject 
adequately  in  a  single  chapter,  but  several  books  are  now  avail- 
able, to  which  foundrymen,  metallurgists  and  chemists  are  referred, 
and  which  are  also  recommended  to  all  engineers,  to  whom  a 
knowledge  of  the  art  is  of  prime  importance. 

236  •': 


IRON   AND   STEEL  FOUNDING 


237 


THE  MAKING  OF  MOLDS 

There  are  various  kinds  of  sand  molds  made  for  foundry  work, 
but  the  three  principal  kinds  are  loam  molds,  dry-sand  molds,  and 
green-sand  molds. 

Loam  Molding.  —  In  molding  with  loam,  sand  is  usually  built 
up  into  the  required  shape  by  hand,  aided  by  machines.  Fig.  185 


FIG.    186.  — MACHINE   FOR   FORMING  THE   TEETH    OF   A  BEVEL-GEAR. 

shows  the  molding  of  a  gear  in  which  the  parts  are  built  up  of 
brick  and  sand  and  then  '  swept'  into  the  proper  shape  by  means 
of  the  wooden  sweeps.  Large  wheels  and  gears  are  often  swept 
up  in  this  way,  the  teeth  being  formed  subsequently  by  means  of  a 
small  pattern  that  is  moved  around  as  the  molder  progresses,  or 


238 


THE  METALLURGY  OF   IRON   AND   STEEL 


by  means  of  a  machine,  as  shown  in  Fig.  186.  In  the  case  of  a  gear, 
the  arms  are  usually  formed  by  placing  within  the  swept-up  mold 
forms  of  sand  known  as  l  cores/  as  shown  in  Fig.  187.  Loam 
molding  is  common  in  iron  foundries,  but  almost  never  used  for 
steel  castings. 

Pattern-Molding.  —  To  only  a  limited  class  of  work  is  loam 
molding  applicable,  and  the  commonest  manner  of  making  a  mold 
is  to  press  or  ram  sand  around  a  pattern,  which  is  subsequently 


FIG.    187. —  PLACING   CORES    IN   A   MOLD. 


removed,  leaving  the  desired  cavity.  Usually  the  pattern  is  en- 
closed by  a  l  flask '  much  larger  than  itself,  between  which  and 
the  pattern  the  damp  sand  is  rammed.  The  pattern  (sometimes)  is 
split  into  halves,  one  half  being  in  the  lower  part,  or  'drag/  of  the 
flask,  and  the  other  half  being  in  the  upper  part,  or  'cope.'1  The 
cope  is  now  taken  off  and  turned  upside  down,  after  which  a  lifting- 
screw  is  inserted  into  each  half  of  the  pattern  in  turn,  by  means  of 

1  The  old  English  word  '  cope/  meaning  a  covering  for  the  head,  which 
has  now  largely  been  replaced  by  the  name  '  cap.' 


240 


THE  METALLURGY  OF   IRON  AND   STEEL 


which  it  is  drawn  from  the  sand ;  and  when  a  '  gate '  is  cut  through 
the  cope,  the  flask  is  again  fastened  together,  and  a  receptacle  is 
formed  of  the  shape  of  the  pattern  into  which  the  metal  may  be 
poured. 

The  art  does  not  consist  of  these  simple  operations  alone,  how- 
ever, for  in  drawing  the  pattern  from  the  sand,  even  though  the 
lifting-screw  be  lightly  tapped  with  a  hammer  in  four  horizontal 
directions  to  loosen  the  pattern,  the  slightest  tremble  of  the  mold- 
er's  hand,  or  of  the  crane  used  for  lifting,  may  cause  the  sand  to  be 


FIG.    192. —  PATTERN   IN   SAND. 

broken  in  places,  and  the  chief  skill  of  the  molder  as  well  as  a  large 
share  of  his  time  is  employed  in  repairing  the  damage  thus  pro- 
duced. Furthermore,  the  mold  may  be  'washed/  that  is,  painted 
inside;  the  proper  cores  must  be  put  in  place;  parts  of  the  sand 
liable  to  drop  off  must  be  nailed  in  place  with  thin,  large-headed 
wire  nails  thrust  in  with  the  thumb ;  before  the  pattern  is  taken  from 
the  sand  the  cope  must  be  l  vented/  that  is,  made  porous,  by 
jamming  a  wire  into  it  many  times  and  pulling  it  out  again,  so  that 
the  air  and  gases  will  escape  when  the  metal  is  poured  in;  and  so  on. 


IRON   AND   STEEL   FOUNDING 


241 


Furthermore,  it  may  readily  be  imagined  that  the  parts  of  the 
pattern  shown  in  Fig.  193  might  be  of  such  a  shape,  with  flanges 
on  the  bottom,  or  something  of  that  kind,  that  they  could  not  be 
drawn  without  breaking  the  sand.  In  the  case  of  such  a  design 
the  pattern  and  flask  must  be  split  into  three  or  more  parts,1  or 
else  a  core  must  be  put  in  to  make  an  offset.  It  will  be  evident  to 


Cheefc 


Cheek 


Drag 
FIG.    193. —  SECTION   OF   FLASK   AND   PATTERN. 

every  engineer  that  he  will  have  to  pay  more  for  making  a  casting 
so  designed. 

Ramming.  —  In  pattern  molding,  it  is  essential  that  the  pres- 
sure of  the  sand  around  the  pattern  shall  be  nearly  uniform  in  all 
places;  because  (1)  when  the  metal  is  poured  into  the  mold,  it 
drives  out  the  air  already  there  by  forcing  it  through  the  inter- 

1  The  bottom  and  top  parts  being  still  known  as  the  'drag'  and  'cope,' 
respectively,  while  the  intermediate  parts  are  known  as  'cheeks.'. 


Finishing  Trowel 


Yankee 


Finishing  Trowel 


Lifter 


Bench  Lifter 


Finishing  Trowel 


Square  Trowel 


FIG.    194. 


Slick  and  Spoon 


IRON  AND  STEEL  FOUNDING  243 

stices  between  the  particles  of  sand,  and  if  the  sand  is  too  hard  in 
any  place,  the  pressure  of  air  collected  there  is  liable  to  form  a  de- 
pression, or  'scab/  in  the  casting;  and  because  (2),  if  the  sand  is 
too  loose  in  any  place,  the  pressure  of  the  metal  upon  it  is  liable  to 
'swell'  it  outward  and  thus  cause  an  enlargement  of  the  casting  at 
that  point.  To  obtain  uniformity  it  is  necessary  that  the  sand  be 
packed  around  the  pattern,  and  not  the  pattern  pushed  into  the 
sand.  This  packing  is  accomplished  by  the  hands  for  the  sand 
immediately  adjacent  to  the  pattern,  and  by  rammers  for  the  lay- 
ers further  distant.  In  the  case  of  bench  molding  hand  rammers 
are  used,  and  for  making  larger  molds  on  the  floor  long  iron  ram- 
mers are  employed.  The  molder's  skill  is  shown  in  applying  the 
proper  amount  of  power  in  ramming  each  different  kind  or  part  of 
pattern. 

Dry-Sand  Molds.  —  After  ramming  up  the  mold,  drawing  the 
pattern  and  applying  the  'wash/  the  mold  may  be  used  green 
(when  it  is  called  a  'green-sand  mold'),  or  it  may  be  put  in  the 
ovens  and  dried  (when  it  is  called  a  '  dry-sand  mold ') .  The  drying 
has  the  effect  of  driving  off  the  moisture  and  leaving  a  firm,  hard 
mass,  semi-baked  into  a  sort  of  brick.  Sand  for  these  molds  should 
have  slightly  more  clay  than  for  green-sand  molds;  otherwise, 
instead  of  baking  into  a  hard  mass,  they  would  be  liable  to  crum- 
ble with  the  heat.  The  temperature  of  drying-ovens  should  be 
about  350°  to  400°  F.  (170°  to  200°  C.),  and  they  are  heated  by 
coke,  coal,  gas,  or  oil.  If  the  temperature  is  too  high,  the  mold 
will  be  burned,  that  is,  it  will  crumble  under  the  fingers  after  drying; 
if  not  hot  enough,  the  mold  will  not  be  baked  hard.  The  length 
of  time  in  the  oven  will  depend  upon  the  size  of  the  mold,  and  will 
vary  from  an  hour  or  so  to  a  day  or  so.  During  the  drying  the 
molds  are  liable  to  shrink  somewhat,  due  to  the  action  of  the  clay 
in  binding  together. 

Green-Sand  Molds.  —  Green  sand  requires  less  clay  than  dry 
sand,  because  it  has  a  certain  coherence  due  to  its  dampness. 
Many  natural  sands  are  found  suitable  for  both  the  green-sand 
mold  and  the  dry-sand  mold,  or  they  can  be  made  up  as  desired 
by  mixing  a  good  clay  with  a  sand  rich  in  silica.  Green-sand 
molds  must  not  be  rammed  as  hard  as  dry  sand,  so  the  moisture 
may  more  readily  evaporate. 

Washes.  —  For  iron  castings  the  common  wash  is  graphite 
dust,  which  is  made  up  into  a  paint  with  water  and  applied  with  a 


IRON   AND   STEEL  FOUNDING  245 

brush  or  dauber  to  the  inside  of  a  dry-sand  mold  before  it  goes  to 
the  oven.  In  the  case  of  a  green-sand  mold,  pulverized  coal  is 
dusted  onto  the  surface  through  a  piece  of  cloth,  and  then  spread 
uniformly  with  the  l  slicker/  In  the  case  of  a  dry-sand  steel  casting, 
the  wash  is  composed  of  pulverized  silica  rock,  running  from  98  to 
99  per  cent,  silica,  which  is  made  up  into  a  thick  paint  with  water, 
thickened  with  molasses,  and  applied  to  the  inside  of  the  mold 
with  a  brush  or  dauber  before  the  mold  is  dried.  Green-sand 
molds  for  steel  castings  cannot  ordinarily  be  washed.  Graphite 
washes  cannot  be  used  for  steel  molds,  because  the  hot  metal 
attacks  the  graphite  and  becomes  rough  upon  its  surface. 

The  functions  of  washes  are :  (1)  To  make  a  very  smooth  face 
on  the  sand,  so  that  the  surface  of  the  casting  shall  be  smooth 
(this  they  accomplish  by  the  very  fine  size  of  their  particles) ;  (2) 
to  give  a  surface  that  shall  resist  the  melting  and  chemical  action 
of  hot  metal,  and  so  be  more  easily  cleaned  of  sand. 

Skin-Dried  Molds.  —  The  inside  surface  of  green-sand  molds  is 
occasionally  dried  by  painting  or  spraying  it  with  some  inflammable 
liquid,  such  as  gasolene,  and  then  applying  a  match.  This  is  more 
common  in  steel-foundry  than  in  iron-foundry  practice,  and  pro- 
duces a  little  better  surface  to  the  casting.  Herbert  B.  Atha 
patented  a  mold  wash  for  green-sand  steel  castings  which  would 
enable  them  to  be  skin  dried.1  The  formula  for  this  wash  was 
devised  by  me  with  the  aid  of  Parker  C.  Mcllhiney.  It  consists 
of  ordinary  gasolene  in  which  is  dissolved  as  much  rosin  as  it  will 
take  up  without  warming.  The  rosin  increases  the  specific  gravity 
of  the  gasolene  so  that  it  forms  a  paint  with  the  silica  wash,  which 
would  otherwise  sink  to  the  bottom  and  not  adhere  to  the  brush. 
After  the  wash  is  applied,  it  is  touched  with  a  match,  the  burning 
resulting  in  giving  a  dry  skin  to  the  mold  and  leaving  it  coated  with 
the  silica.  The  rosin  does  not  completely  burn  off,  but  binds  the 
sand  together  and  gives  a  tough  skin,  so  that  the  sand  is  not  so 
liable  to  drop  when  the  cope  is  turned  over  to  place  it  upon  the 
drag. 

Dry-  versus  Green-Sand  Molds:  For  Iron  Castings.  —  (1)  Dry- 
sand  molds  are  often  cheaper  to  make  and  require  less  molding 
skill,  because  the  sand  does  not  have  to  be  tempered  so  carefully, 
that  is,  brought  to  the  proper  condition  of  dampness,  since  the 

»U.  S.  Letters  Patent  No.  686,189. 


246 


THE  METALLURGY   OF   IRON   AND   STEEL 


moisture  is  eventually  to  be  driven  off  by  the  drying.  In  green- 
sand  molds,  if  the  sand  is  too  wet,  it  is  liable  to  '  cut'  (be  eroded  by 
the  stream  of  metal)  and  get  dirt  into  the  casting,  and  also  to  be 
impervious  to  the  gases.  (2)  The  sand  requires  less  care  in  ram- 
ming, because,  whether  too  hard  or  too  soft,  the  expansion  and 
contraction  in  drying  will  adjust  its  firmness  and  porosity.  (3) 
Furthermore,  the  dry  sand  is  stronger,  which  is  an  advantage, 
especially  in  large  castings  or  when  the  sand  is  liable  to  be  under 


FIG.   196.  — CORES   FOR  FORMING  THE   INSIDE  OF  A  GAS-ENGINE 
CYLINDER   CASTING. 

pressure  from  the  metal,  or  to  have  the  metal  fall  upon  it  from  a 
height.  (4)  Dry-sand  castings  are  also  more  liable  to  be  sound, 
because  there  is  less  gas  in  the  pores  of  the  sand. 

The  disadvantages  of  dry-sand  castings  are:  (1)  The  mold  is 
liable  to  shrink  during  drying  and  therefore  be  less  true  to  the  pat- 
tern; (2)  the  castings  are  more  liable  to  'check'  (that  is,  crack  in 
cooling),  because  the  mold  is  firmer  and  so  does  not  give  way  so 
easily  to  the  crushing  action  when  the  casting  contracts;  (3)  molds 
exposed  to  the  direct  action  of  the  flame  during  drying,  or  heated 


IRON  AND   STEEL  FOUNDING 


247 


too  hot,  are  liable  to  be  burnt  and  therefore  rendered  useless,  caus- 
ing a  loss;  (4)  in  handling,  the  molds  are  liable  to  be  damaged; 
and,  furthermore,  it  is  more  costly  to  repair  a  dry  mold  than  a 
damp  one,  because  the  adjacent  sand  must  first  be  damped,  the 


FIG.    197. —  CORE. 

damage  repaired,  and  then  a  flame  applied  to  dry  the  wound;  (5) 
it  takes  longer  to  complete  an  order.  The  actual  cost  of  heat  is 
not  very  great,  and  usually  is  less  of  an  item  than  the  extra  labor 
of  handling  for  drying. 

For  Steel  Castings.  —  Dry-sand  steel  castings  have  a  surface 
much  superior  to  those  made  in  green  sand.1  They  are  also 
stronger  and  more  liable  to  be  sound.  Soundness  is  much  more 


FIG.    198. 

difficult  to  obtain  in  steel  castings  than  in  iron  castings.     Green- 
sand  molds,  however,  have  the  great  advantage  of  allowing  their 

1  The  reason  that  dry-sand  steel  castings  have  a  better  surface  is  because 
they  can  be  washed.  In  practice,  however,  the  drying  and  washing  is  often 
improperly  performed;  therefore  green-sand  castings  often  have  the  better 
surface. 


248 


THE  METALLURGY  OF   IRON  AND  STEEL 


sand  to  crush  more  easily  when  between  two  parts  of  the  casting 
that  are  being  drawn  together  by  the  shrinking  of  the  metal. 
This  is  doubly  advantageous  in  steel  work,  because  steel  shrinks 
twice  as  much  as  cast  iron  and  is  therefore  more  liable  to  checking. 


FIG.    199. 


Special  means  may  be  employed  for  making  the  sand  easily  col- 
lapsible after  the  metal  is  poured,  such  as  mixing  with  it  an  in- 
flammable substance  like  flour,  chopped  hay,  hay-rope,  sawdust, 
etc.,  which  burns  away  after  the  hot  metal  is  poured  in. 


FIG.  200. 


Cores.  — The  function  of  cores  has  already  been  referred  to: 
they  are  set  inside  the  mold  proper  to  assist  in  forming  the  metal. 
The  commonest  use  for  them  is  to  extend  through  a  casting  in  some 
place  to  make  a  hole,  as,  for  instance,  the  inside  of  a  cylinder,  the 


IRON   AND   STEEL   FOUNDING 


249 


bore  of  a  pulley,  etc.  In  this  position  they  are  subjected  to 
great  crushing  strain  when  the  metal  shrinks,  and  therefore  the 
bond  which  keeps  the  sand  together,  consisting  of  linseed-oil,  or 
flour  paste,  a  patented  core  compound,  etc.,  must  be  of  such  a 
nature  that  when  subjected  to  the  heat  of  the  liquid  metal  it  will 
burn  away  and  allow  the  sand  to  disintegrate,  which  both  prevents 
it  bursting  the  shrinking  casting  and  permits  of  its  being  more 
easily  cleaned  out.  Cores  are  often  built  up  around  an  iron  pipe 


FIG.  201.  — OVEN  FOR  DRYING  SMALL  CORES. 

riddled  with  holes,  so  that  the  gases  formed  may  readily  escape 
through  this  'vent.'  In  the  case  of  large  cores,  the  pipe  is  fre- 
quently wound  with  hay-rope,  or  some  similar  material  that  will 
burn  away  and  make  the  sand  more  collapsible.  Some  cores  have 
coke  breeze  or  cinder  in  the  center  to  make  them  light  as  well  as 
porous. 

Cores  are  supported  sometimes  by  being  set  in  the  drag,  some- 
times by  being  hung  in  the  cope  (see  Fig.  202) ;  but  it  is  more  com- 


250 


THE   METALLURGY  OF   IRON  AND   STEEL 


mon  to  have  a  hollow  adjunct  to  the  mold,  known  as  a  '  core-print/ 
into  which  an  extension  of  the  core  fits  (see  Fig.  190).     Some- 


FIG.  202.  — CORES  HUNG  FROM  THE  COPE. 


FIG.  203.  —  CHAPLETS. 


times  both  ends  of  the  core  are  so  supported,  and  sometimes  only 
one  end  is  thus  supported,  while  the  other  end  rests  upon  a  metal 


FIG.   204.  —  POSITION   OF   MACHINE   WHEN   PRESSING   THE   DRAG. 


FIG.   205.  —  POSITION  OF  MACHINE  WHEN  PRESSING  THE  COPE. 


FIG.  206.  —  CUTTING   SPRUE   WITH    TUBULAR   SPRUE   CUTTER, 


PIG.    207.  — RAPPING   THE    PATTERN    BEFORE    SEPARATING    THE    MOLD. 


IRON   AND   STEEL  FOUNDING 


253 


chaplet  that  is  absorbed  in  the  casting  when  the  metal  is  poured. 
Cores  are  often  dried,  lest  their  gases  make  the  casting  unsound 
or  cause  it  to  blow,  that  is,  boil  with  the  rapid  escape  of  gas  through 
the  metal. 

Chill  Molds.  —  It  is  often  desired  to  chill  certain  parts  of  a 
mold,  or  cool  them  more  rapidly  than  the  remainder,  in  order  either 
to  make  a  thick  part  of  a  casting  solidify  as  soon,  or  sooner,  than 
the  thinner  portions,  or  else  to  produce  white  cast  iron  at  that 
point.  The  former  may  be  desirable  in  the  case  of  either  an  iron 


FIG.    208.  —  STRIPPING   PLATE 
MOLDING   MACHINE. 


FIG.    209.  —  STRIPPING   PLATE 
MOLDING   MACHINE. 


or  steel  casting,  because  the  shrinkage  cavity  occurs  in  the  last 
portion  to  freeze,  and  therefore  hastening  local  freezing  may  be 
necessary  to  bring  the  pipe  into  the  riser  or  feeder.  The  latter 
applies  only  in  iron-casting  work  in  which  it  is  desired  to  make 
the  outside  of  a  casting  very  hard.  The  chilling  is  usually  accom- 
plished by  embedding  pieces  of  metal  in  the  sand,  against  the  face 
of  which  the  casting  is  poured.  This  metal  is  oiled,  blackened  or 
'  washed/  so  that  it  does  not  stick  to  the  casting. 

Permanent  Molds.  —  A  great  deal  of  expense  in  foundry  work 
is  due  to  the  fact  that  a  sand  mold  must  be  made  anew  for  every 
casting,  and  the  subject  of  permanent  molds  has  occupied  the 
attention  of  foundrymen  for  a  great  many  years  without  the  prob- 


FIG.   210. 


FIG.    211. 


IRON   AND   STEEL   FOUNDING  255 

lem  being  solved.  When  a  casting  is  knocked  out  of  the  mold, 
the  sand  is  usually  knocked  out  also  and  its  form  destroyed.  In 
the  rare  case  of  a  smooth  cylinder,  or  something  of  that  kind,  the 
casting  may  be  withdrawn  without  damage  except  to  the  face  of 
the  sand,  and  this  can  sometimes  be  repaired  and  swept  up  anew 
without  reforming  the  entire  mold.  Again,  molds  for  railroad  car 
wheels,  which  have  a  metal '  chill'  all  the  way  round  the  tread  and 
flange,  in  order  that  the  cast  iron  may  be  white  at  that  point  to 
withstand  the  grinding  action  on  the  rails,  have  a  certain  amount 


FIG.    212.  —  ROCK-OVER   MOLDING   MACHINE. 

of  permanency.  Finally,  molds  carved  out  of  carbon  which  has 
been  preheated  to  a  very  high  temperature  are  said  to  withstand 
the  action  of  the  melted  metal  and  to  last  for  a  large  number  of 
castings. 

Gated  Patterns.  —  Where  the  castings  are  very  small,  a  large 
number  of  them  will  be  made  into  one  pattern,  fastened  onto  a 
common  'gate'  through  which  they  are  poured,  which  produces 
very  great  economy  in  molding. 

Molding  Machines.  —  At  the  present  time  various  types  of 


Upper  head  swung  back  to  receive  flask.     Drag  patterns  on  upper  head. 
Cope  patterns  on  lower  head.  Yoke  swung  by  power. 


Sand  frame  on  flask. 
FIGS.   213  AND  214.  —  VIBRATOR   MOLDING   MACHINE. 


Mold  removed,  flask  frame  raised,  showing  method  of  drawing  cope  patterns. 


Mold  lowered  away,  drawing  drag  patterns.     Drag  patterns  may  be 

returned  with  absolute  accuracy. 
FIGS.  215  AND  216.  — VIBRATOR  MOLDING  MACHINE. 


258  THE  METALLURGY  OF   IRON  AND   STEEL 

i 

molding  machines  are  being  extensively  introduced  into  foundries, 

in  order  to  save  some  of  the  labor  or  skill  required  in  molding,  or 
both.  The  simplest  form  of  machine  is  the  'squeezer/  which 
may  be  described  by  reference  to  Fig.  204.  The  correct  amount  of 
sand  is  poured  into  the  flask  and  by  means  of  a  long  lever  the 
'presser  board'  is  forced  down  on  top  of  this  sand,  squeezing 
it  around  the  pattern  and  producing  a  half  mold.  In  taking 
the  flask  off  the  pattern  by  hand,  damage  may  be  done  the  sand, 
and  the  molder's  skill  is  still  required  to  repair  it. 


: :  ^l^i^HR 

FIG.    217. —VIBRATOR. 

The  stripping-plate  machine  obviates  part  of  this  difficulty, 
however.  In  this  type  the  half  pattern  may  be  pushed  up  or 
down  through  a  close-fitting  hole  in  a  plate  known  as  the  '  strip- 
ping-plate'  (see  Fig.  211).  After  the  sand  has  been  rammed 
around  the  pattern,  a  lever  draws  the  pattern  down  through 
the  stripping-plate.  As  this  drawing  is  mathematically  exact, 
no  damage  results  to  the  sand  and  no  repairs  to  the  mold  are 
necessary,  so  that  unskilled  laborers  may  be  employed  for  the  work. 

A  still  further  extension  in  the  line  of  machines  is  the  '  vibra- 


IRON   AND   STEEL  FOUNDING 


259 


tor/  whereby  the  pattern  is  vibrated  an  extremely  small  amount, 
some  5000  to  30,000  times  per  minute,  during  the  drawing  of  the 
pattern.  No  stripping-plate  is  necessary  to  separate  it  from  the 
sand,  since  the  vibrator  frees  it  perfectly  and  without  damage. 

In  all  these  molding  machines  the  operation  may  be  conducted 
either  by  means  of  levers,  or  by  a  mechanism  operated  by  hydrau- 
lic or  pneumatic  power,  and  several  hundred  patterns  may  be 
made  per  day  by  one  man  who  is  very  little,  if  any,  more  skilled 
than  a  common  laborer;  and  machines  are  made  in  which  castings 


FIG.    218. —CORE    MACHINE   AND   CORES. 

weighing  from  a  couple  of  ounces  to  several  hundred  pounds  may 
be  molded  with  great  economy. 

Core  Machines.  —  There  are  also  on  the  market  several  machines 
for  making  cores,  an  example  of  which  is  shown  in  Fig.  218. 

Multiple  Molds.  —  During  the  past  year  or  two  a  new  type  of 
molding,  known  as  '  multiple  molding/  has  come  into  use,  in  which 
several  flasks  are  placed  in  a  pile  and  poured  through  a  common 
gate  of  sprue,  as  shown  in  Fig.  219.  This  type  of  molding  saves 
mold  costs,  flasks,  sand,  floor  space,  and  the  weight  of  metal 
wasted  in  sprues,  and  many  difficulties  have  been  overcome,  so 


260 


THE   METALLURGY  OF   IRON   AND   STEEL 


that  the  castings  are  now  made  accurately  to  size  and  good  in  all 
respects. 

Shrinkage.  —  A  bar  of  cast  iron  12  in.  long  will  contract  about 
0.125  in.  during  solidification  and  cooling  (i.e.,  it  will  be  about  llf 
in.  long  when  cold.  See  page  346  for  further  details),  while  a  bar 


FIGS.    219  AND  220.  —  MULTIPLE   MOLD   AND   CASTING. 

of  steel  will  contract  about  twice  as  much.     In  both  cases  the 
contraction  in  sectional  dimensions  will  not  be  as  great  as  in  length. 


DESIGN  OF  PATTERNS 

The  foregoing  description  will  show  what  a  great  financial 
advantage  it  is  to  a  purchaser  if  he  designs  castings  that  can  be 
easily  molded,  and  if  he  can  order  a  large  number  of  castings  of 
exactly  the  same  design.  It  is  certain  that  a  hundred  castings 
of  one  design  can  be  made  with  very  much  greater  cheapness  than 
the  same  number  all  of  different  designs,  and  of  this  economy  the 
purchaser  obtains  his  full  share,  because  the  foundry  is  glad  to 
encourage  such  a  customer  and  to  make  concessions  in  order  to  do 
his  work.  I  cannot  recommend  too  strongly  to  engineers  the 
practice  of  making  the  castings  in  all  similar  machines  inter- 
changeable, both  for  the  sake  of  economy  and  of  avoiding  some 


IRON   AND   STEEL   FOUNDING  261 

delay  and  expense  in  replacement  after  a  breakdown.  The  correct 
design  of  castings  is  furthermore  one  of  the  most  important 
branches  of  engineering  work,  since  the  number  of  castings  used 
is  almost  one-half  of  the  total  number  of  pieces  used  in  engineering 
work,  while  their  weight  is  equal  to  about  one-sixth  of  the  weight  of 
all  the  iron  and  steel  employed.  The  following,  general  hints  are 
therefore  offered  to  assist  in  this  design ;  but  each  casting  is  a  study 
in  itself,  in  order  that  the  various  desiderata  referred  to  may  be 
obtained. 

To  Avoid  Checks.  —  The  commonest  error  in  engineering  de- 
signs of  castings  is  to  make  the  corners  too  sharp,  which  makes 
them  very  liable  to  check,  because  of  the  crystalline  character  of 
iron  and  steel.  This  is  the  more  important,  because  the  greatest 
leverage  comes  at  the  corners,  which  therefore  should  be  made  as 
strong  as  possible.  Metals  are  crys- 
talline substances  and  the  crystals  grow 
during  solidification.  As  solidification 
usually  extends  from  the  surface  in- 
ward, the  crystals  grow  in  a  direction 
perpendicular  to  the  cooling  surfaces. 
As  shown  in  Fig.  221,  this  results  in  a 
line  extending  inward  from  all  corners, 
marking  the  junction  of  many  crystals. 
As  the  junction  lines  of  crystals  are  FIG.  221. 

not  as  strong  as  the  crystals  themselves, 

this  makes  a  line  of  weakness  on  corners,  which  is  the  more  marked 
the  sharper  the  corner  is.  In  case  a  casting  is  to  be  machined, 
it  is  much  better  to  put  a  large  fillet  in  all  the  corners,  even  if  the 
rounded  metal  must  be  cut  away  later,  as  greater  strength  is 
obtained  in  this  way. 

The  checking  of  castings  comes  from  the  strain  produced  by 
the  shrinkage  of  the  metal  tending  to  crush  the  sand.  This  is 
the  more  intense  the  greater  the  distance  is  between  the  two 
crushing  parts,  because  they  must  approach  each  other  by  an 
amount  exactly  proportional  to  the  length  of  metal  between  them. 
It  is  therefore  wise,  wherever  possible,  to  avoid  long  lengths  of 
metal  connecting  two  parts  which  project  into  the  sand. 

Unequal  cooling  strains  will  also  cause  a  check.  This  may  be 
illustrated  by  a  pulley  with  thick  arms  and  a  thin  face.  The  face 
will  solidify  first  and  therefore  yield  very  little  to  the  subsequent 


262  THE  METALLURGY  OF   IRON  AND   STEEL 

shrinkage  of  the  arms.  Moreover,  the  face,  being  cooler,  will  be 
stronger  and  the  tendency  will  be  for  the  arms  to  tear  themselves 
in  two.  To  avoid  this  it  is  common  practice  to  chill  the  arms 
either  by  setting  metallic  pieces  in  the  mold,  or  by  means  of  a 
'  water  gate/  A  water  gate  is  a  loose  column  of  coke  molded  into 
the  sand  of  the  cope  down  which  water  may  be  poured. 

To  Avoid  Shrinkage  Cavities.  —  The  formation  of  a  '  pipe'  or 
shrinkage  cavity  has  already  been  explained.  Such  a  defect  in  a 
casting  would  be  intolerable,  and  is  commonly  avoided  by  having 
a  reservoir  of  metal  situated  above  the  casting  proper  and  large 
enough  to  keep  it  supplied  with  molten  metal  until  it  has  com- 
pletely solidified.  This  reservoir  is  known  as  the  '  riser/  or 
' header'  (sometimes  merely  'head'),  or  'feeder.'  The  riser  is 
included  as  a  part  of  the  mold  when  it  is  made,  but  is  cut  off 
the  finished  casting  and  used  over  again  as  scrap.  Sometimes 
castings  are  so  designed  by  engineers  that  a  heavy  section  of  metal 
must  be  molded  underneath  a  thinner  section.  As  the  thinner 
section  will  solidify  first,  it  cannot l  feed '  this  lower,  heavy  section ; 
and  therefore  a  special  form  of  riser  is  required,  or  else  the  heavier 
section  must  be  artificially  cooled. 

CUPOLA  MELTING  OF  IRON  FOR  CASTINGS 

Iron  for  castings  is  melted  either  in  the  cupola  or  the  air  fur- 
nace, although  'direct  castings,'  i.e.,  castings  made  from  the  metal 
just  as  it  comes  out  of  the  blast  furnace,  are  used  in  many  cases, 
and  especially  for  cast-iron  ingot  molds  at  steel-works.  There 
are  men  with  sufficient  expertness  to  be  able  to  judge  by  eye  the 
character  and  the  analysis  of  the  liquid  iron  as  it  flows  from  the 
furnace,  and  this  is  necessary  where  direct  castings  are  to  be  made, 
because  the  metal  may  vary  greatly  and  without  warning  from 
one  cast  to  another.  In  this  work,  however,  metal  mixers  are 
sometimes  used,  similar  to  those  at  steel-works. 

The  Cupola  Furnace.  —  The  design  and  principle  of  operation 
of  the  cupola  furnace  bears  some  similarity  to  that  of  the  blast 
furnace,  the  chief  difference  being  that  the  coke  of  the  cupola  fur- 
nace is  desired  only  for  its  melting  influence,  and  that  the  only 
chemical  reactions  are  minor  ones  and  unintentional.  The  cupola 
affords  the  cheapest  method  of  melting  metals,  because  there  is 
direct  contact  between  the  metal  and  fuel  and  therefore  the  maxi- 


Layer  of 
Iron 


Layer  of 
Coke 


Layer  of 
Iron 


Layer  of 
Coke 


Layer  of 
Iron 


iim 


Iron 


FIG.    222. —  IRON   CUPOLA. 


264  THE  METALLURGY  OF   IRON  AND  STEEL 

mum  absorption  of  heat.  The  most  usual  amounts  of  fuel  burned 
will  be  from  one-fourth  to  one-twelfth  of  the  weight  of  the  iron 
melted,  the  former  figure  prevailing  where  exceedingly  hot  metal 
is  desired  —  as,  for  example,  for  very  small  castings  for  malle- 
able cast-iron  work  —  and  the  latter  figure  where  the  melting  is 
continued  for  several  hours  and  the  metal  is  not  made  very  hot, 
but  is  to  be  poured  into  large  castings. 

Cupola  Zones.  —  The  cupola  should  be  so  operated  that  cer- 
tain well-defined  zones  of  action  are  maintained,  in  order  that 
rapid,  hot  and  economical  melting  may  be  obtained  and  that  loss 
by  oxidation  may  be  small.  If  proper  conditions  prevail  all  of 
these  desiderata  may  be  obtained  together,  while,  if  otherwise, 
wasteful  methods  may  be  accompanied  by  slow,  irregular  melting 
and  'dull  iron/  i.e.,  iron  not  sufficiently  hot.  The  management 
of  the  cupola  is  too  often  neglected  and  left  in  the  hands  of  men 
who  understand  nothing  of  its  proper  operation,  and  whose  only 
skill  consists  in  knowing  how  to  perform  certain  manual  opera- 
tions. If  the  iron  is  coming  too  cold  (which  may  actually  be  due 
to  too  much  coke  having  been  used  in  the  charges),  their  stock 
remedy  is  to  put  in  more  coke.  The  result  is  slow  melting  and 
probably  still  colder  iron.  At  once  an  earnest  complaint  goes  to 
the  office  of  the  bad  quality  of  the  coke.  To  get  faster  melting, 
however,  the  blast  pressure  is  increased ;  now  the  iron  comes  faster 
and  hotter,  and  the  office  is  informed  that  "we  have  worked  off 
that  bad  lot  of  coke."  If  the  manager  becomes  doubtful  and 
orders  less  coke  used,  every  wrong  thing  that  happens  in  the  foun- 
dry thereafter  is  blamed  to  that  order,  until  the  manager  decides 
that  coke  is  cheaper  than  dissatisfaction  and  tells  the  cupola  man 
to  follow  his  own  discretion. 

All  this  is  wrong.  The  cupola  deserves  the  oversight  of  a  man 
who  is  capable  of  understanding  its  operation  and  who  will  give 
real  thought  to  it,  and  not  be  satisfied  with  blind  rules  of  thumb. 

The  zones  of  action  which,  I  have  said,  are  so  important  in  this 
connection  are,  beginning  at  the  bottom  of  the  cupola  and  going 
upward:  (1)  The  crucible  zone,  or  hearth;  (2)  the  tuyere  zone; 
(3)  the  melting  zone;  and  (4)  the  stack.  The  cupola  is  filled  with 
alternate  layers  of  coke  and  iron,  as  shown  in  Fig.  222, x  and  the 
different  zones  are  produced  by  the  action  of  the  blast  and  the 

1  Except,  of  course,  during  the  intervals  of  starting  up  arid  blowing  out. 


FIGS.    223  TO  227.  —  FOUNDRY   LADLES. 


266  THE  METALLURGY  OF   IRON  AND   STEEL 

heat  upon  these  different  layers.  The  thickness  of  these  layers 
should  be  the  same  in  large  as  in  small  cupolas. 

Crucible  Zone.  —  The  crucible  extends  from  the  bottom  of  the 
cupola  to  the  level  of  the  tuyeres.  The  sole  object  of  this  part  is  to 
form  a  place  in  which  the  iron  and  slag  may  collect  after  they  have 
melted  and  trickled  down  to  the  bottom.  If  the  tap-hole  is  kept 
open  all  the  time  and  the  metal  allowed  to  flow  out  of  the  cupola 
and  collect  in  an  outside  ladle  as  fast  as  it  melts,  the  crucible  zone 
will  be  very  shallow,  and  the  tuyeres  will  be  situated  not  more 
than  two  to  five  inches  above  the  bottom.  If,  on  the  other  hand, 
the  crucible  is  used  as  a  reservoir  for  a  large  amount  of  metal,  the 
tuyeres  are  placed  correspondingly  high.  Hotter  metal  may  be 
obtained  by  collecting  the  iron  in  an  outside  ladle. 

Tuyere  Zone.  —  The  tuyere  zone  is  the  place  in  which  the  blast 
comes  in  contact  with,  and  burns,  the  red-hot  coke.  It  is  the  zone 
of  combustion,  and  all  the  heat  of  the  operation  should  be  pro- 
duced in  this  place.  It  is  of  course  situated  near  the  tuyeres  and 
wherever  the  blast  may  come  in  contact  with  coke.  As  there  is 
always  a  column  of  coke  extending  from  the  melting  zone  to  the 
very  bottom  of  the  cupola,  combustion  will  begin  immediately 
above  the  reservoir  of  melted  metal.  The  upper  limit  of  the  com- 
bustion zone  will  depend  upon  the  pressure  of  blast,  because  the 
greater  the  blast  pressure,  everything  else  being  the  same,  the 
higher  will  it  extend  its  zone  of  combustion.  The  blast  pressure 
should  be  such,  however,  that  the  top  of  the  tuyere  zone,  or  zone 
of  combustion,  should  never  be  more  than  15  to  24  in.  above  the 
uppermost  tuyeres.1 

Melting  Zone.  —  The  melting  zone  is  the  space  in  which  all 
the  melting  of  iron  takes  place;  it  is  situated  immediately  above 
the  tuyere  zone.  During  the  melting  the  iron  is  supported  on  a 
column  of  coke  which  extends  to  the  bottom  of  the  cupola,  and 
which  is  the  only  solid  material  below  the  melting  zone.  When 
each  layer  or  charge  of  iron  enters  the  melting  zone  it  should  be 
about  15  to  24  in.  above  the  uppermost  tuyeres.  As  fast  as  it 
melts  it  trickles  down  over  the  column  of  coke  to  the  bottom.  It 
takes  about  five  to  ten  minutes  for  each  layer  of  iron  to  melt,  how- 
ever, and  during  this  time  the  column  of  coke  is  burning  and  sink- 
ing. Therefore,  the  last  of  the  iron  will  melt  at  a  point  about 

1  There  are  sometimes  two  rows  of  tuyeres  in  cupolas;  see  page  268. 


IRON  AND  STEEL  FOUNDING 


267 


7  in.  lower  than  the  first.  Consequently,  the  melting  zone  over- 
laps the  upper  limit  of  the  zone  of  combustion.  If  the  layers  of 
iron  and  coke  are  properly  proportioned  to  the  pressure  of  blast, 


Tuyere 
Tap  Hole 


FIG.   228. 


FIG.    229. 


each  charge  of  iron  will  enter  the  top  of  the  melting  zone  just 
before  the  next  previous  charge  is  completely  melted  at  the  bottom, 
and  thus  a  continuous  stream  of  iron  will  collect  in  the  crucible 
or  run  from  the  tap-hole.  Also,  the  coke  burned  from  the  column 


268 


THE  METALLURGY  OF   IRON  AND  STEEL 


will  be  exactly  replenished  each  time  by  the  layer  of  coke  coming 
down,  and  the  position  of  the  melting  zone,  which  is  the  important 
consideration,  will  be  maintained  within  constant  limits. 

The  actual  position  of  the  melting  zone  may  always  be  learned 
when  the  cupola  is  emptied,  because  the  iron  oxide  formed  there 
will  corrode  the  acid  lining,  which  will  therefore  be  cut  away  some- 
what at  this  point.  Corrections  may  then  be  made,  if  necessary,  in 
the  next  charge  of  the  cupola. 

Stack.  —  The  stack  extends  above  the  melting  zone  to  the  level 
of  the  charging  door.  The  function  of  this  part  of  the  furnace  is 


FIG.    230.  —  POSITIVE   PRESSURE    IMPELLOR   BLOWER. 

to  contain  material  that  will  absorb  heat  and  thus  prepare  itself 
for  the  actions  at  lower  levels,  and  that  will  also  keep  the  heat 
down  in  the  melting  zone  as  well  as  possible. 

Tuyeres.  —  The  blast  enters  the  cupola  through  the  tuyeres,  of 
which  there  is  usually  one  or  two  rows.  The  position  of  the  upper 
row  of  tuyeres  determines  the  position  of  the  melting  zone  in  the 
cupola.  Two  rows  of  tuyeres  give  faster  melting  in  the  cupola 
than  one  row,  but  cause  greater  oxidation  and  the  consumption 
of  more  fuel  on  the  bed,  because  of  the  melting  zone  being  higher 
in  the  cupola. 

Blast.  —  The  blast  pressure  will  depend  somewhat  upon  the 
size  of  the  cupola,  but  the  present  prevailing  opinion  is  in  favor 


IRON  AND  STEEL  FOUNDING 


269 


of  pressures  not  exceeding  a  pound,  even  for  the  very  largest 
cupolas,  and  diminishing  to  half  a  pound  or  so  for  the  smaller 
sizes.  Fan-blowers  are  not  approved  of,  because  if  they  are 
opposed  by  pressure  in  the  cupola  stack,  they  revolve  with- 
out blowing  any  wind.  The  common  type  of  blower  used  in 
America  is  of  the  two-impellor  type,  an  example  of  which  is  shown 
in  Fig.  231.  It  takes  about  60  cu.  ft.  of  air  to  burn  a  pound  of  coke, 
from  which  may  be  calculated  the  size  of  blower  necessary  for  each 


FIG.    231. 


cupola,  allowing  about  50  to  100  per  cent,  excess  for  leaks  and 
incomplete  combustion. 

Makers  of  cupolas  and  blowers  give  all  the  necessary  data  in 
their  catalogues,  but  advocate  too  high  blast  pressures  and  vol- 
umes, for  obvious  reasons.  If  the  blast  volume  is  too  large,  or  the 
pressure  is  too  great,  the  position  of  the  melting  zone  will  be  too 
high.  This  means  that  the  bed  of  coke  must  be  larger  to  reach  to 
the  upper  level  of  the  melting  zone,  which  is  wasteful.  It  also 


270  THE  METALLURGY   OF  IRON   AND   STEEL 

means  'that  the  melted  iron  will  have  a  greater  height  to  drop 
through.  It  therefore  oxidizes  more,  corrodes  the  cupola  lining 
more,  and  consequently  causes  more  waste  of  iron  and  more  slag. 
The  volume  of  blast  is  the  most  important  consideration,  but  this 
is  difficult  to  measure,  so  the  pressure  is  the  thing  that  is  calculated 
upon.  It  must  be  remembered,  however,  that  this  is  only  a 
makeshift  arrangement  at  the  best. 

Cupola  Charge.  —  In  the  cupola  is  first  placed  shavings  and 
wood,  on  top  of  which  is  placed  the  bed  of  coke,  which  should  be 
large  enough  to  reach  15  to  24  in.  above  the  uppermost  tuyeres 
after  the  kindling  is  burned  off.  On  top  of  this  is  placed  a  layer 
of  pig  iron  about  6  in.  thick,  then  another  layer  of  coke  about  7  in. 
thick,  another  layer  of  iron,  and  so  on.  The  actual  weight 
of  the  coke  for  the  bed  and  of  coke  and  iron  for  each  charge  will 
therefore  depend  directly  upon  the  diameter  of  the  cupola  inside 
the  brick  lining,  which  varies  from  about  32  to  120  in.,  or  even 
more  in  some  cases.  The  weight  of  the  coke  in  each  layer  will  be 
about  one-sixth  to  one-twelfth  of  the  weight  of  iron  in  each 
layer.  The  tuyeres  and  front  of  the  cupola  around  the  tap-hole, 
known  as  the  'breast/  are  left  open  for  an  hour  or  so  after  the 
kindling  is  lighted,  in  order  that  the  draft  may  draw  air  in  at  that 
point  for  combustion.  When  the  kindling  is  thus  burned  off 
and  the  bottom  coke  well  lighted;  the  breast  is  closed  and  the 
wind  turned  on.  It  is  very  necessary  that  the  bed  should  be 
well  lighted  and  level. 

Cupola  Melting.  —  The  heat  now  generated  by  the  combustion 
of  coke  begins  to  melt  the  iron,  and  in  less  than  15  minutes  after  the 
wind  is  put  on  the  metal  should  begin  to  run  from  the  open  tap- 
hole.  If  it  takes  longer,  then  the  coke  bed  was  too  high  and  waste- 
ful. In  another  8  to  10  minutes  the  first  layer  of  iron  should 
be  all  melted.  Now  the  second  layer  of  iron  lies  upon  the  column 
of  coke,  whose  top  should  again  be  15  to  24  in.  above  the  upper- 
most tuyeres.  If  the  layers  of  coke  are  too  thick  there  will  be  a 
delay  in  the  iron  entering  the  melting  zone  and  the  extra  coke 
burned  will  not  have  been  used  to  the  best  account.  If  the  layers 
of  iron  are  too  thick,  the  last  of  the  layer  will  melt  too  near  the 
tuyeres,  which  will  oxidize  it  excessively  and  make  it  cold.  This 
can  be  observed  during  the  run  by  noting  if  the  iron  nms  first  hot 
and  then  cold.  It  is  very  important  to  watch  the  flame  that  comes 
off  the  top  of  the  stack  in  the  cupola.  When  the  blast  volume  is 


IRON  AND   STEEL  FOUNDING  271 

too  large  this  flame  will  be  '  cutting/  —  i.e.,  oxidizing  in  character. 
Too  great  oxidation  may  also  be  observed  if  sparks  of  burning  iron 
are  projected  from  the  slag-hole.  If  the  layers  of  iron  and  coke 
are  both  too  thick,  there  may  be  a  correct  relation  between  the 
weights  of  the  two,  but  both  of  the  irregularities  mentioned  above 
will  be  observed.  If  the  layers  of  iron  and  coke  are  both  too  thin, 
we  will  have  two  charges  of  iron  in  the  melting  zone  at  the  same 
time,  and  this  may  be  learned  by  watching  the  iron  from  the  tap- 
hole,  because  it  will  run  at  some  times  faster  than  at  other  times. 
This  does  not  produce  such  bad  results,  however,  as  having  the 
layers  too  thick.  Of  course,  if  very  hot  iron  is  required  it  will 
be  necessary  to  have  thicker  layers  of  coke,  and  slower  melting 
must  be  expected. 

Chemical  Changes.  —  As  the  iron  drops  down  over  the  coke,  it 
absorbs  sulphur,  the  exact  proportion  depending  chiefly  upon  the 
relative  amount  of  coke  and  iron  used  and  the  per  cent,  of  sulphur 
in  the  coke.  It  will  vary  from  0.02  to  0.035  per  cent,  of  the  iron; 
that  is  to  say,  if  the  pig  iron  charged  contained  0.08  per  cent,  sul- 
phur, there  will  be  from  0.1  to  0.115  per  cent,  in  the  castings.  The 
sulphur  in  the  first  iron  will  be  higher  than  in  that  of  the  middle  of 
the  run,  because  of  the  extra  amount  of  coke  burned  before  the 
iron  begins  to  come  from  the  tap-hole.  The  last  iron  will  also  be 
somewhat  higher  in  sulphur,  because  there  is  a  larger  loss  of  metal 
during  the  last  of  the  run,  when  the  oxidizing  conditions  are  more 
intense,  and  therefore  a  concentration  of  sulphur.  The  best 
practice  is  to  cut  the  blast  off  progressively  as  there  is  less  stock 
in  the  cupola. 

In  many  foundries  it  is  customary  to  charge  limestone,  in  the 
form  of  oyster  shells,  marble  chippings,  or  crude  limestone,  and 
sometimes  with  it  a  little  fluorspar  (CaF2),  into  the  cupola.  The 
amount  of  limestone  varies  greatly,  but  will  average  perhaps  J  to  1J 
per  cent,  of  the  weight  of  the  metal.  This  limestone  fluxes  the  dirt 
on  the  metal  and  the  ash  of  the  coke  and  carries  off  some  sulphur  in 
the  slag.  Fluorspar  makes  a  somewhat  more  liquid  slag  than 
limestone  alone  and  the  more  liquid  slag  is  believed  to  absorb  a 
little  more  sulphur,  and  also  to  make  the  cupola  'drop'  more 
easily,  i.e.,  dump  its  contents  when  the  campaign  is  ended,  and 
the  bottom  is  allowed  to  fall.  It  also  cuts  the  lining  more. 

As  the  metal  melts  and  falls  from  the  melting  zone  down  in 
front  of  the  tuyeres,  it  suffers  oxidation,  which  carries  iron  oxide 


272  THE  METALLURGY  OF  IRON  AND  STEEL 

into  the  slag  and  also  burns  up  silicon.  The  melted  metal  there- 
fore contains  from  0.25  to  0.4  per  cent,  less  silicon  than  the  original 
pig.1  In  other  words,  if  the  mixture  charged  contains  2.25  per 
cent,  of  silicon,  the  castings  will  contain  1.85  to  2  per  cent,  silicon. 
Cupola  Gases.  —  The  gases  coming  out  of  the  top  of  the  cupola 
charge  consist  principally  of  nitrogen  from  the  air,  while  the 
remainder  is  carbon  dioxide — COa — and  carbon  monoxide — CO — 
with  sometimes  a  little  free  oxygen.  The  latter  is  evidence  of  a 
'cutting  flame'  and  shows  too  great  oxidation  in  the  melting 
zone.  Such  a  flame  may  be  recognized  without  the  aid  of  chemical 
analysis  after  a  little  practice  by  means  of  the  eye.  It  is  '  sharper ' 
looking  than  a  richer  flame  and  burns  close  to  the  top  of  the  stock. 
One  can  identify  it  exactly  by  holding  an  iron  rod  in  it  for  a 
while;  after  the  iron  becomes  red  hot  it  will  oxidize  much  more 
rapidly  in  a  cutting  flame  than  in  a  reducing  flame.  A  reducing 
flame  will  usually  not  burn  until  it  becomes  mixed  with  the  air 
sucked  in  at  the  charging  door.  All  the  carbon  monoxide  that 
goes  out  of  the  charge  represents  incomplete  combustion  and  a 
waste  of  heat.  It  seems  to  be  impossible  to  prevent  this  here, 
however,  just  as  in  the  blast  furnace,  whose  operations  cupola 
melting  resembles  in  some  general  respects.  Several  analyses 
of  cupola  gases  are  given  in  Table  XVIII. 

1  With  good  practice  it  should  be  no  more  than  0.30  per  cent.  less. 


IRON  AND   STEEL  FOUNDING 


273 


TABLE  XVIIL— ANALYSIS  OF  CUPOLA  GASES 
COLLECTED  ABOUT  3  OR  4  FEET  BELOW  THE  CHARGING  DOOR 


Time  Elapsed  Since 
Blast  was  Put  on 

ANALYSIS  BY  VOLUME 

Oxygen 
O 

Carbon 
Dioxide 
CO2 

Carbonic 
Oxide 
CO 

Nitrogen  (by 
Difference) 

N 

Ratio 
CO2  is  to  CO 
as  1  is  to: 

10  minutes 

0.0 

13.8 

9.9 

76.3 

0.717 

1  hour     13        " 

0.0 

9.5 

16.9 

73.6 

1.780 

2  hours    17        " 

0.4 

9.2 

16.6 

73.8 

1.804 

3       "      13 

0.0 

6.7 

21.7 

71.6 

3.239 

4       "      15 

0.1 

7.8 

22.3 

69.8 

2.859 

38 

1.8 

7.6 

15.5 

75.1 

2.04 

1  hour     42 

2.8 

7.5 

13.3 

76.4 

1.77 

2  hours   50        " 

1.9 

7.1 

15.8 

75.2 

2.225 

3       "      40 

0.1 

7.2 

19.0 

73.7 

2.64 

38        " 

0.0 

10.2 

14.6 

75.2 

1.431 

3       " 

2.9 

5.4 

14.3 

77.4 

2.65 

10 

0.2 

13.1 

7.7 

79.0 

0.588 

3       "      10 

0.3 

10.3 

11.7 

77.7 

1.136 

50 

0.0 

7.1 

15.4 

77.5 

2.17  • 

1  hour     40 

0.0 

8.3 

13.5 

78.2 

1.626 

2  hours   40 

0.0 

8.2 

12.1 

79.7 

1.475 

3       "      40 

0.0 

6.0 

15.0 

79.0 

2.50 

45 

0.0 

13.0 

12.6 

74.4 

0.97 

1  hour     40 

0.0 

13.0 

11.2 

75.8 

0.862 

2  hours   40 

0.0 

8.2 

20.0 

71.8 

2.44 

3       "      50 

0.4 

6.0 

22.1 

71.5 

3.683 

4       "      43 

1.2 

5.1 

21.2 

72.5 

4.157 

1  hour 

0.0 

9.8 

15.4 

74.8 

1.571 

1       "      53       " 

0.0 

9.1 

16.8 

74.1 

1.846 

2  hours  45 

0.0 

8.8 

16.8 

74.4 

1.91 

3       "      45 

0.0 

7.5 

19.7 

72.8 

2.627 

4       "      45 

0.0 

7.5 

18.7 

73.8 

2.500 

ANOTHER  CUPOLA 


30 

0.1 

16.7 

7.3 

75.9 

.437 

Ihour     30 

0.1 

13.1 

10.7 

76.1 

.817 

2  hours   38 

0.4 

11.8 

11.0 

76.8 

.932 

3       "      20 

0.0 

12.8 

7.7 

79.5 

.602 

Burdening  the  Cupola.  —  It  should  be  the  duty  of  the  foundry 
metallurgist  or  chemist  to  learn  from  his  records,  or  other  ap- 
proximations, the  amount  and  analysis  of  all  the  metal  in  the 


274 


THE   METALLURGY  OF   IRON  AND   STEEL 


yard.     The  following  table  will,  for  example,  show  a  convenient 
form  of  this  record. 

TABLE  XIX 


KIND 

Weight 
Tons 

Si 

s 

P 

Mn 

Price 

High  Sulphur,  Southern 
High  Silicon,  Bessemer  . 
XNo.  1  
No.  3  Foundry  

500 
60 
100 
150 

0.70 
2.50 
3.00 
1.75 

0.100 
0.025 
0.030 
0.070 

1.50 
0.07 
0.80 
0  30 

0.30 
0.60 
1.25 
0  60 

$18.00 
25.00 
24.00 
22  50 

Ferrosilicon  A  

30 

10.00 

0.040 

0  50 

0.10 

35  00 

Ferrosilicon  B 

30 

50  00 

0  003 

0  04 

105  00 

Machinery  Scrap  

100 

1.70? 

0.100? 

1.00? 

0.60? 

19  00 

Miscellaneous  Scrap  
Cast-iron  Borings     .  .  . 

300 
100 

1.50? 
1  50? 

0.20? 
0  20? 

1.40? 
1  40? 

0.60? 
0  60? 

15.00 
11  00 

Steel  Scrap  

100 

0  10 

0  07 

0  10 

0  60 

13  00 

The  price  should  always  be  in  evidence.  It  should  not  be  the 
price  at  which  the  material  was  purchased  but  the  market  price 
at  the  time  the  iron  is  to  be  used.  For  instance,  if  a  large  amount 
of  high  grade  pig  iron  had  been  contracted  for  a  year  previously 
and  if  meanwhile  the  price  of  pig  iron  had  been  rising,  the  pur- 
chase price  of  that  pig  iron  would  not  represent  its  present  value. 
From  the  current  numbers  of  such  trade  periodicals  as  the  Iron 
Age  and  the  Iron  Trade  Review,  one  can  always  obtain  the  pre- 
vailing prices  for  the  different  grades  of  iron. 

Suppose  now  with  these  irons  it  is  desired  to  burden  a  72-in. 
cupola  with  a  mixture  for  making  heavy  hydraulic  pumps  for 
which  a  satisfactory  analysis  might  be  1.60  per  cent,  silicon, 
0.70  per  cent,  phosphorus,  less  than  0.10  per  cent,  sulphur  and 
about  0.50  per  cent,  manganese.  The  first  step  is  to  calculate 
the  cupola  charges,  and  the  chemist  knows  by  experience  with 
this  particular  cupola  that  it  will  lose  0.25  per  cent,  silicon  and 
0.10  per  cent,  manganese  and  it  will  gain  0.03  per  cent,  sulphur. 
The  average  analysis  of  the  mixture  put  into  the  cupola  must  then 
be  1.85  per  cent,  silicon,  0.70  per  cent,  phosphorus,  less  than 
0.07  per  cent,  sulphur  and  about  0.60  per  cent,  manganese.  The 
chemist  also  knows  by  calculation  that  about  5200  Ibs.  of  iron 
will  give  a  layer  of  the  proper  thickness  in  a  72-in.  cupola.  His 
problem  now  is  to  make  such  a  mixture  of  the  available  pig  irons 
that  their  collective  weight  will  be  5200  Ibs.  and  their  average 
analysis  as  given  above.  Moreover  if  he  is  a  good  metallurgist 


IRON   AND   STEEL   FOUNDING  275 

he  must  aim  at  using  as  large  an  amount  as  possible  of  the  cheapest 
materials. 

He  first  considers  the  steel  scrap,  but  knows  he  cannot  use 
very  much  of  this  because  too  much  coke  would  be  required  for 
getting  iron  of  the  requisite  fluidity,  but  he  estimates  that  5  per 
cent,  (say  200  Ibs.)  will  not  increase  harmfully  the  fuel  necessary. 
This  figure  therefore  comes  at  the  top  of  his  list  (see  Table  XX). 

Next  he  considers  the  use  of  machinery  scrap,  because  he 
knows  that  his  miscellaneous  scrap  and  borings  are  too  uncertain 
in  analysis  to  be  used  in  a  mixture  which  must  give  pretty  strong 
and  non-porous  castings.  One  thousand  pounds  of  machinery 
scrap  would  be  about  20  per  cent,  of  his  mixture,  and  he  knows 
from  experience  that  this  is  a  fairly  satisfactory  proportion  for 
scrap,  so  that  figure  goes  down  second  in  Table  XX.  The  low 
price  of  the  High  Sulphur  Southern  Pig  tempts  him,  but  he 
realizes  that  he  must  offset  the  use  of  this  material  by  some  high 
silicon  low  sulphur  iron.  And  in  casting  about  for  such  a  one 
he  naturally  considers  first  the  X  No.  1.  He  cannot  use  much 
of  this  either  because  of  its  high  manganese  and  it  seems  reason- 
able to  mix  an  equal  amount  of  these  two;  the  only  question  is, 
How  much  of  this  mixture  will  the  cupola  stand  ?  To  get  an  idea 
of  this,  he  first  calculates  their  average  analysis  and  finds  it  to 
be  1.85  per  cent,  silicon,  0.065  per  cent,  sulphur,  1.15  per  cent, 
phosphorus,  and  0.78  per  cent,  manganese.  Evidently  the  phos- 
phorus is  the  only  element  in  this  mixture  that  gives  him  difficulty. 
Indeed,  if  that  were  not  high  he  could  make  almost  his  whole 
charge  up  of  these  two  irons  and  the  scrap.  The  phosphorus  in 
this  mixture  is  0.45  per  cent,  higher  than  that  of  his  desired 
mixture.  Therefore  he  knows  that  he  must  use  a  good  deal  of 
No.  3  Foundry  iron  to  bring  this  element  down.  The  phosphorus 
in  the  No.  3  Foundry  iron  is  about  as  much  below  the  desired 
phosphorus  as  that  in  the  mixture  of  the  High  Sulphur  Southern 
and  the  X  No.  1  is  above  it  He  must  not  forget,  however, 
that  he  has  already  used  1000  Ibs.  of  machinery  scrap  containing 
probably  1  per  cent,  of  phosphorus.  Therefore  he  must  use  a 
correspondingly  larger  amount  of  No.  3  iron  to  offset  this  also. 
As  a  first  estimate  he  therefore  considers  using  800  Ibs.  of  High 
Sulphur  Southern,  800  Ibs.  of  X  No.  1,  and  2400  Ibs.  of  No.  3 
Foundry — that  is,  once  and  a  half  as  much  No.  3  as  the  mixture 
of  the  other  two.  But  a  little  reflection  tells  him  that  this  mixture 


276  THE  METALLURGY  OF   IRON  AND   STEEL 

is  going  to  be  too  low  in  silicon,  because  the  mixture  of  High 
Sulphur  Southern  and  X  No.  1  only  gave  us  1.85  per  cent,  silicon, 
while  the  No.  3  foundry  and  the  machinery  scrap  are  both  below 
that.  There  are  then  three  ways  open  to  him.  He  may  use  a 
little  Ferrosilicon  A  or  he  may  pound  up  a  little  Ferrosilicon  B 
and  dissolve  it  in  the  ladle  of  iron  or  he  may  use  a  little  High 
Silicon  Bessemer  iron.  Either  of  these  methods  would  do,  but  the 
writer  would  prefer  to  use  the  High  Silicon  Bessemer  because  this 
will  have  the  effect  of  cutting  the  sulphur  and  phosphorus  down 
and  the  expense  is  practically  the  same.  (It  requires  such  a  small 
amount  of  ferrosllicon  to  give  the  desired  silicon  in  the  mixture 
that  the  expense  of  using  it  is  very  small,  in  spite  of  its  price.) 
Consequently  we  put  down  the  weights  shown  in  the  second  column 
of  Table  XX,  and  we  now  figure  out  the  weight  of  silicon,  sulphur, 
phosphorus,  and  manganese  in  the  mixture  by  the  methods 
indicated  there,  and  the  average  percentage  of  each  element. 
The  latter  figures  show  us  that  the  silicon  is  too  low,  and  a  simple 
calculation  shows  us  that  we  need  5  Ibs.  more  in  the  total  weight 
of  silicon.  We  can  get  this  by  increasing  the  amount  of  either 
High  Silicon  Bessemer  or  of  X  No.  1,  and  correspondingly  de- 
creasing the  No.  3  Foundry.  The  High  Silicon  Bessemer  has 
0.75  per  cent,  more  silicon  than  the  No.  3,  so  it  would  take  (5  Ibs. 
-5-0.75  per  cent.=)  about  650  Ibs.  change  to  make  up  the  difference 
in  this  way.  The  X  No.  1  has  1.25  per  cent,  more  silicon  than  the 
No.  3,  so  it  would  take  (5  Ibs. -7-1.25=)  400  Ibs.  change  to  make 
up  the  difference  in  this  way.  We  naturally  would  prefer  to  use 
the  latter,  being  cheaper,  and  if  we  think  we  can  stand  all  that 
extra  manganese  in  our  castings  we  probably  will  do  so;  if  not, 
we  will  have  to  use  altogether  1000  Ibs.  of  High  Silicon  Bessemer 
and  only  1400  Ibs.  of  No.  3  Foundry.  We  then  make  up  a  new 
table  similar  to  Table  XX  and  figure  out  the  average  analysis  as 
before.  It  should  now  come  about  right. 


IRON   AND   STEEL   FOUNDING 


277 


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278  THE  METALLURGY  OF   IRON  AND  STEEL 

LOSSf  __  The  loss  in  melting  will  average  about  2  to  4  per'  cent. 
It  is  made  up  of  the  silicon  burned  and  the  iron  oxidized  and  car- 
ried away  in  the  slag.  There  are  other  sources  of  loss  in  the 
foundry,  such  as  a  second  loss  of  metal  remelted  —  the  sprues, 
risers,  etc.,  which  go  back  to  the  cupola  in  the  form  of  scrap; 
metal  spilled  during  pouring  (which  may  amount  to  as  much  as 
5  or  6  per  cent,  more),  etc.  In  some  foundries  it  is  customary  to 
pass  the  used  floor  sand  through  a  magnetic  concentrator,  in 
order  to  recover  the  pellets  of  iron  spilled 
during  pouring,  and  important  economy 
is  sometimes  obtained  in  this  way.  The 
total  loss,  that  is,  the  difference  in  weight 
between  pig  iron  bought  and  castings 
made,  will  probably  be  about  7  to  8  per 
cent,  of  the  weight  of  the  iron  bought. 

Scrap  Used.  —  Scrap  pig  iron  is  often 
mixed  with  new  pig  iron  for  the  manu- 
facture of  castings,  both  for  the  sake  of 
economy  and  because  the  scrap  iron  has  a 
somewhat  closer  grain  or  texture,  which 

FIG.   232.  —  MAGNETIC  ,,  ^      f  ,-,  .     ,  i™ 

CONCENTRATOR.  increases  the  strength  of  the  mixture.  I  he 

amount  of  scrap  used  will  depend  upon  the 

materials  to  be  manufactured.  Cast-iron  pipe  is  usually  made 
without  scrap,  this  industry  amounting  to  between  500,000  and 
800,000  tons  per  year  in  the  United  States  alone.  Stove  foundries, 
on  the  other  hand,  use  a  very  large  amount  of  scrap  as  a  rule,  and 
jobbing  foundries,  in  general,  would  probably  use  an  average  of 
30  to  40  per  cent,  of  outside  scrap,  besides  the  gates,  sprues,  bad 
castings,  etc.,  made  in  their  own  foundries.  The  total  production 
of  gray-iron  castings  in  the  United  States  will  represent  about 
75  per  cent,  pig  iron  and  25  per  cent,  bought  scrap.1 

Cupola  Run.  —  The  campaign  of  an  ordinary  foundry  cupola 
is  only  three  or  four  hours  long.  As  a  general  thing,  the  kindling 
is  started  about  noon  and  allowed  to  burn  with  a  natural  draft 
until  shortly  after  one  o'clock,  when  the  breast  is  closed  and  the 
blast  put  on.  Metal  is  then  received  until  four  or  five  o'clock  in 
the  afternoon,  when  the  last  charge  is  melted.  The  supports  are 
then  pulled  out  from  underneath  the  door  closing  the  bottom  of 

1  For  these  estimates,  I  am  indebted  to  Henry  M.  Lane,  editor  of  Castings, 
in  a  private  communication  of  Nov.  30,  1906. 


IRON  AND  STEEL  FOUNDING  279 

the  cupola,  and  the  sand  bottom,  slag,  coke,  etc.,  left  in  the  cupola 
is  allowed  to  drop  and  is  quenched  with  water.  In  order  to  allow 
plenty  of  room  for  the  'drop'  to  fall,  the  cupola  is  usually  ele- 
vated above  the  foundry  floor. 

COMPAKATIVE    CUPOLA    PRACTICE 

After  writing  the  foregoing  discussion,  some  very  valuable 
figures  on  "Comparative  Cupola  Practice'7  were  presented  by 
W.  S.  McQuillan  to  the  Philadelphia  Convention  of  the  Ameri- 
can Foundrymen's  Association.  The  figures  there  given  were 
of  very  great  interest  and  value  (see  the  Foundry,  July,  1907, 
pp.  370  to  373),  and  confirm  in  a  striking  way  the  rules  I  have 
laid  down  above.  I  have  copied  a  part  of  this  table  in  my  ac- 
companying Table  XXI  and  added  several  lines  to  it.  I  have 
also  had  all  the  calculations  in  the  table  checked  up  by  two  in- 
dependent observers. 

Fuel.  —  The  first  lesson  we  learn  from  the  table  is  that  a 
mixture  of  coal  and  coke  and  inferior  coke  give  slow  melting 
and  a  poor  fuel  ratio.  Indeed,  the  work  of  the  cupola  using  these 
grades  of  fuel  is  so  far  inferior  to  the  others  that  I  have  separated 
them  in  Table  XXI  and  omitted  them  from  all  my  calculations. 
After  a  very  careful  study  of  the  figures,  I  am  strengthened  in  the 
opinion  which  I  have  long  held  and  expressed  that  a  mixture  of 
coal  and  coke  has  nothing  to  recommend  it  except  a  deceptive 
first  cost. 

Tuyere  Ratio.  —  The  next  most  striking  evidence  produced 
by  the  figures  is  the  relation  between  the  tuyere  area  and  the 
speed  of  melting:  if  we  average  up  the  iron  melted  per  minute  in 
the  cupolas  whose  area  is  less  than  6.56  times  the  tuyere  area, 
we  obtain  a  figure  of  22.56  Ibs.;  if  we  get  the  corresponding  figure 
for  the  cupolas  with  lesser  proportionnte  tuyere  area,  we  obtain 
18.57  Ibs.  Indeed  so  striking  is  the  relation  that  there  is  only 
one  exception,  namely,  cupola  No;  8,  and  we  need  not  look  far 
for  a  reason  for  the  slow  melting  in  this  cupola.  It  is  evidently 
due  to  the  short  height  of  stack  which  causes  the  iron  to  reach  the 
melting  zone  before  it  has  been  sufficiently  preheated.  A  large 
proportionate  tuyere  area  evidently  means  that  the  wind  will  pass 
through  the  tuyeres  with  less  resistance  and  a  lower  velocity. 
That  is  to  say,  we  will  get  more  wind  and  it  will  not  be  driven  so 


280  THE  METALLURGY  OF   IRON  AND   STEEL 

TABLE  XXI.— COMPARATIVE  CUPOLA  PRACTICE 


1 

2 

3 

4 

5 

Diameter  of  cupola,  inches.  .  .  . 
Height  of    tuyeres  from  sand 
bottom,  inches  

27 
12 

35 

7 

42 
11 

44 
12 

54 
7.5 

Height  of  charging  door  above 
tuyeres,  inches  

106 

120 

139 

109 

103.5 

Height  of  charging  door  above 
tuyeres  divided  by  diameter. 
Number  of  tuyeres 

4.0 
6 

3.4 
6 

3.3 
6 

2.5 

1.9 
6 

Size  of  tuyeres,  inches,  vertical 
X  horizontal.  .  . 

4x6 

5x5 

4x6 

4^x13 

Area  of  tuyeres,  square  inches  . 
Cupola  area  is  how  many  times 
tuyere  area  

144 
3.97 

170 
5.661 

144 
9.62 

336 
4  53 

348 
6  58 

Diameter  of  blast  pipe,  inches  . 
Blast  pressure,  ounces,  20  min- 
utes after  start 

8 
9 

16 
16 

14 
8 

15 
<U 

17 
13 

Class  of  work  made                   •< 

Job 

Plate 

Light 

Boiler 

Stove 

Lined  up  how  often?    Months 

6 

Job 
6 

&  Plate 
6 

Plate 
6 

Weight  of  fuel  on  bed,  pounds. 
Weight  of  iron  on  bed,  pounds. 
Weight  of  fuel  in  charges  sub- 
sequent to  the  bed,  pounds.  . 
Weight  of  iron  in  charges  sub- 
sequent to  the  bed,  pounds.  . 
Total  weight  of  fuel,  pounds.  .  . 
Total  weight  of  iron,  pounds.  .  . 
Ratio  of  fuel  on    bed,  above 
tuyeres,  to  iron   on  bed,  1 
is  to  

350 
700 

90 

400 
2,000 
8,000 

3  2 

650 
1,300 

125 

1,300 
1,850 
14,000 

2  8 

650 
1,400 

100 

1,000 
2,150 
16,000 

Q    K 

1,300 
3,000 

175 

2,000 
3,075 
27,000 

3  2 

1,400 
3,000 

300 

3,000 
4,800 
33,000 

3  7 

Ratio   of  fuel    to    iron,   later 
charges  

4  4 

10  4 

10  0 

11  4 

10  0 

One    pound    fuel    melts    how 
many  pounds  iron  

4  0 

7  5 

7  6 

8  8 

•_^ 
6  9 

Kind  of  fuel  used  -j 

Coke 

Coke 

Coke 

Coke 

Coke 

Fuel  weighed  or  measured  
Height    of     fuel    bed    above 
tuyeres,  inches.  .  . 

W 
20 

W 
21  1 

M 
1^ 

W 

QQ 

W 
24 

Thickness  of  fuel,  charges  after 
the  bed,  inches  

8  4 

7  0 

Q    8 

6    1 

6  9 

Thickness  of  iron  charges  after 
the  bed,  inches  

3  3 

6  5 

3  5 

6  3 

6  3 

Time  before  iron  comes   after 
blast  is  on,  minutes  
Time  to  melt  each  iron  charge 
after  the  bed,  minutes  .... 

7 
3  25 

15 
8  5 

5 

5  7 

15 
9 

10 
10 

Total  iron  melted  per  minute, 
pounds  

123 

1  Pjr; 

22  *> 

QOO 

Total  iron  melted  per  minute, 
per  square  foot  cupola  area  . 

30.98 

23.20 

18.19 

21.30 

18.87 

1Two  rows  of  tuyeres. 


IRON   AND  STEEL  FOUNDING  281 

TABLE  XXL— COMPARATIVE  CUPOLA  PRACTICE.— Continued 


6 

7 

8 

9 

10 

11 

Diameter  of  cupola,  inches  .... 
Height  of  tuyeres  from  sand 
bottom,  inches         

54 
14 

56 
25 

58 
16 

60 
2 

60 
12 

72 
24 

Height  of  charging  door  above 
tuyeres  inches 

113 

141 

92 

112 

114 

142 

Height  of  charging  door  above 
tuyeres  divided  by  diameter  . 
Number  of  tuyeres 

2.1 
6 

2.5 
12 

1.6 
6 

1.9 

8 

1.9 
6 

2.U 

Size  of  tuyeres,  inches,  vertical 
X  horizontal   

10x7 

6x12 

7x12 

4Jx7i 

7x10 

Area  of  tuyeres,  square  inches  . 
Cupola  area  is  how  many  times 
tuyere  area                  

420 
5.45 

864 
2  85 

546 

4.831 

270 
10  47 

420 
6  73 

706 
5  76 

Diameter  of  blast  pipe,  inches  . 
Blast  pressure,  ounces,  20  min- 
utes after  start   

18 
14 

24 
16 

20 
16 

18 
8 

18 
8 

24 
13£ 

Boiler 
& 

Rolls 

Pipe 

Ft'g& 

Plate 

Sanitary 
& 

Elec- 

Lined up  how  often?     Months  . 
Weight  of  fuel  on  bed,  pounds  . 
Weight  of  iron  on  bed,  pounds  . 
Weight  of  fuel  in  charges  sub- 
sequent to  the  bed,  pounds  .  . 
Weight  of  iron  in  charges  sub- 
sequent to  the  bed,  pounds  .  . 
Total  weight  of  fuel,  pounds  .  .  . 
Total  weight  of  iron,  pounds.  .  . 
Ratio  of  fuel  on  bed,   above 
tuyeres,  to  iron  on  bed,   1 
is  to          

Radiator 
10 
2,000 
6,000 

450 

4,000 
8,500 
64,800 

4.3 

8  to  10 
3,000 
9,000 

450 

4,500 
12,000 
100,000 

5  0 

Job 
7  • 
2,000 
6,000 

400 

4,000 
4,400 
30,000 

5  0 

6 
1,700 
6,000 

200 

2,000 
6,600 
49,500 

3  8 

Plate 
12 
1,800 
5,000 

350 

4,000 
6,600 
50,000 

4  7 

trical 

6 
2,500 
7,000 

600 

7,600 
12,700 
127,500 

5  4 

Ratio   of   fuel    to    iron,    later 
charges       

8.8 

10  0 

4  1 

10  0 

11  4 

11  7 

One    pound    fuel    melts    how 
many  pounds  iron  

7.5 

8  3 

6  8 

7  5 

7  6 

10  0 

Kind  of  fuel  used  •] 

Coke 

Coke 

Coke 

Coke 

Coke 

Solvay 

Fuel  weighed  or  measured  .... 
Height    of    fuel     bed     above 
tuyeres,  inches  

M 
32 

W 

40 

W 

14  1 

M 
30 

W 
22 

Coke 
W 

6 

Thickness  of  fuel,  charges  after 
the  bed,  inches  

10.4 

9.6 

8.0 

3.8 

6.5 

7  8 

Thickness  of  iron  charges  after 
the  bed,  inches  

8.4 

8.8 

7.3 

3.4 

6.8 

9 

Time  before  iron  conies  after 
blast  is  on,  minutes  
Time  to  melt  each  iron  charge 
after  the  bed,  minutes  
Total  iron  melted  per  minute, 
pounds  

20 
11 
360 

5 
12 
370 

15 
12 
333 

1 
5.5 
367 

15 
11 
360 

15 
13.5 
567 

Total  iron  melted  per  minute, 
per  square  foot  cupola  area. 

22.64 

21.60 

18.14 

18.80 

18.40 

20.06 

JTwo  rows  of  tuyeres. 


(For  averages,  see  next  page.) 


282  THE  METALLURGY  OF  IRON  AND   STEEL 

TABLE  XXL— COMPARATIVE  CUPOLA   PRACTICE.— Continued 


Al 

A2 

A3 

A4 

Averages 

Diameter  of  cupola  inches..    . 

32 

42 

44 

48 

Height  of  tuyeres  from  sand 
bottom,  inches  

11 

12 

9.5 

14 

12.  61 

Height  of  charging  door  above 
tuyeres  inches 

133 

132 

84  5 

103 

116 

Height  of  charging  door  above 
tuyeres  divided  by  diameter  . 
Number  of  tuyeres     

4.1 
6 

3.1 
6 

1.9" 

8 

2.1 
6 

2.52 

Size  of  tuyeres,  inches,  vertical 
X  horizontal  

4£x6 

4x10 

2Jxll 

4x6 

Area  of  tuyeres  square  inches 

162 

240 

198 

144 

Cupola  area  is  how  many  times 
tuyere  area                         . 

4  96 

5  77 

7  68 

12  56 

6  56  l 

Diameter  of  blast  pipe  inches 

12 

14 

12 

16 

Blast  pressure,  ounces,  20  min- 
utes after  start  

16 

12 

13 

8 

12  l 

Class  of  work  made         .        •< 

Gas 

Job 

Pumps 

Medium 

Lined  up  how  often''*    Months 

Engine 
6 

&  Job 
3 

Light 
6 

Weight  of  fuel  on  bed,  pounds  . 
\Veight  of  iron  on  bed  pounds 

450 
1  000 

1,000 
4500 

1,000 
1  000 

1,300 
4000 



Weight  of  fuel  in  charges  sub- 
sequent to  the  bed  pounds 

110 

250 

110 

200 

Weight  of  iron  in  charges  sub- 
sequent to  the  bed  pounds 

1  000 

2000 

1  500 

2000 

Total  weight  of  fuel  pounds 

1  250 

1  935 

2  040 

4  100 

Total  weight  of  iron  pounds 

8  000 

12  000 

14800 

32  000 

Ratio  of  fuel  on  bed,   above 
tuyeres,  to  iron  on  bed,  1 
is  to 

3  5 

8  6 

1  6 

5  0 

4  2 

Ratio   of   fuel   to    iron,    later 
charges      

8  7 

8  0 

13  6 

10  0 

9  5 

One    pound    fuel    melts    how 
many  pounds  iron  

6  4 

6  2 

7  2 

7  8 

7.31 

Kind  of  fuel  used  •< 

Fuel  weighed  or  measured  .... 
Height     of    fuel     bed     above 
tuyeres,  inches 

Light 
Coke 
M 

21 

Coal& 
Coke 
M 

11 

Coal& 
Coke 
W 

25 

Coke& 
Coal 
M 

22  5 

22  51 

Thickness  of  fuel,  charges  after 
the  bed,  inches  

7  3 

9  5 

3  9 

5  8 

7  O1 

Thickness  of  iron  charges  after 
the  bed,  inches 

6 

4  7 

5  3 

6  41 

Time  before  iron  comes  after 
blast  is  on,  minutes  
Time  to  melt  each  iron  charge 
after  the  bed,  minutes  
Total  iron  melted  per  minute, 
pounds  

10 

7.7 
57 

15 

15 
9.5 
164 

7 
13.8 
145 

11.  31 
9.46i 

Total  iron  melted  per  minute, 
per  square  foot  cupola  area  . 

10  2 

15  53 

11  54 

21.  II2 

Including  Al,  A2,  A3,  A4. 


2  Excluding  Al,  A2,  A3,  A4. 


IRON  AND   STEEL  FOUNDING  283 

much  to  the  center  of  the  cupola.  If  the  publication  of  these 
figures  did  no  more  good  than  to  point  out  the  advantage  of  the 
large  tuyere  area,  they  would  have  already  contributed  a  very 
great  deal  to  the  foundry  industry.  It  may  be  said  to  be  established 
for  the  types  of  practice  here  exhibited  that  the  collective  area  of 
the  tuyeres  should  not  be  less  than  one-sixth,  and  preferably  not 
less  than  one-quarter,  of  the  horizontal  area  of  section  of  the 
cupola. 

Height  of  Stack.  —  There  is  also  an  important  relation  between 
the  speed  of  melting  and  the  height  of  the  charging  door  above 
the  tuyeres  divided  by  the  diameter  of  the  cupola.  The  average 
speed  of  melting  of  the  cupolas,  where  this  ratio  is  greater  than 
2.5,  is  24.12  Ibs.  per  minute,  while  the  average  speed  of  melting 
of  those  whose  ratio  is  less  than  2.5  is  only  19.15  Ibs.  per  minute. 
There  are  only  two  exceptions  to  this  rule:  (1)  Cupola  No.  6  is 
a  fast  melter,  but  this  is  doubtless  due  to  the  large  proportionate 
tuyere  area.  (2)  Cupola  No.  3  is  a  slow  melter,  but  this  is  doubt- 
less due  to  the  very  small  proportionate  tuyere  area.  With  these 
exceptions  the  rule  is  universal  and  a  comparison  of  different 
cupolas  one  with  another  only  strengthens  it;. for  example,  4  with 
8,  the  proportionate  tuyere  area  being  nearly  the  same;  also 
2  with  6,  etc.  A  comparison  of  3  with  9  is  an  apparent  exception 
which  is  perhaps  explained  by  the  low  tuyeres  in  No.  9. 

Blast  Pressure.  —  The  average  speed  of  melting  of  the  cupolas 
with  more  than  12  oz.  blast  pressure  is  only  20.75  Ibs.  per  minute, 
while  that  with  less  than  12  oz.  is  21.53.  This  relation  is  not 
so  striking  as  to  establish  a  rule,  especially  as  a  single  cupola 
(No.  1)  throws  such  a  large  influence  into  the  low-blast  column. 
Nevertheless,  the  evidence  is  sufficiently  striking  to  discredit 
the  theory  that  higher  blast  pressure  necessarily  gives  faster 
melting.  Indeed,  if  cupolas  3,  9,  and  10  had  a  larger  tuyere  area, 
we  should  expect  an  average  result  very  favorable  to  low  blast 
pressure. 

Height  of  Fuel  Bed.  —  The  original  height  of  fuel  bed  is  no 
criterion  with  which  to  figure  as  it  in  many  cases  is  raised  or 
lowered  during  the  first  few  minutes  of  melting,  and  thereafter 
occupies  some  other  position.  It  is  the  thickness  of  the  fuel  and 
iron  charges  after  the  bed  which  is  the  important  consideration 
and,  as  already  observed,  these  should  be  regulated  to  about 
6  to  8  in.  for  fuel  and  6  in.  for  iron  irrespective  of  the  diameter  of 


284  THE  METALLURGY  OF   IRON  AND   STEEL 

the  cupola.     In  case  hot  iron  is  desired  the  layer  of  fuel  should  be 
at  the  upper  limit  of  thickness  and  vice  versa. 

Speed  of  Melting.  —  The  speed  of  melting  is  very  important, 
because  everything  else  being  equal  the  faster  the  melting  per 
square  foot  of  cupola  area  the  greater  will  be  the  efficiency  of 
operation  of  the  cupola,  and  therefore  of  economy  under  the 
given  conditions. 

OTHER  MELTING  FURNACES 

Air-Furnace.  —  The  air-furnace  is  a  reverberatory  furnace  on 
the  hearth  of  which  pig  iron  is  melted  by  radiation  from  the  flame 
of  a  soft-coal  fire,  or,  more  rarely,  from  a  gas  flame.  The  furnace 
is  charged  by  means  of  a  large  side  door,  or  by  removing  the  roof 
in  sections  bound  together  with  iron,  or  by  taking  out  the  end,  and 
in  some  cases,  to  effect  an  economy  in  labor,  mechanical  devices 
are  employed  for  charging.  Several  designs  of  air-furnaces  are 
shown  in  Figs.  266  to  269  inclusive. 

Cupola  versus  Air-Furnace  Melting.  —  The  air-furnace  is  not 
as  economical  of  fuel  as  the  cupola,  and  the  amount  of  coal  used 
will  average  about  one-fifth  to  one-third  of  the  weight  of  the  iron 
melted.  The  air-furnace  has,  however,  some  very  important  ad- 
vantages which  enable  it  to  produce  a  higher  quality  of  castings: 
(1)  The  metal  does  not  absorb  so  much  sulphur,  since  it  is  not 
in  contact  with  the  fuel  and  can  only  take  up  sulphur  from  the 
furnace  gases;  air-furnace  iron  will  therefore  increase  only  about 
0.001  to  0.008  per  cent,  in  sulphur;  (2)  the  control  of  its  com- 
position in  silicon  and  carbon  is  much  better,  as  by  retaining 
it  for  a  longer  time  in  the  furnace  after  melting  we  may  burn 
out  any  desired  amount  of  these  elements.  Therefore,  when 
making  iron  which  must  be  reduced  in  silicon  or  carbon,  as, 
for  example,  metal  for  malleable  cast-iron  castings,  or  when 
making  iron  that  must  be  very  close  to  a  certain  analysis,  as, 
for  example,  cast  iron  that  is  to  be  chilled  on  the  surface  (for 
instance,  railroad  car  wheels,  rolls  for  reducing  the  size  of  metal 
bodies,  etc.),  the  air-furnace  is  very  commonly  used;  (3)  air-* 
furnace  iron  is  stronger  than  cupola  iron  on  account  of  lower  total 
carbon  and  sulphur  and  better  control  generally. 

Operation  of  Air-Furnace.  —  Forced  draft  is  usually  used  for 
the  fire,  and  sometimes  additional  air  is  introduced  just  above  the 


IRON  AND   STEEL  FOUNDING  285 

fire-bridge,  in  order  to  increase  the  oxidizing  effect  of  the  flame. 
There  are  also  doors  in  the  side  walls  for  the  same  purpose.  It 
takes  from  about  3J  to  9  hours  to  melt  down  a  charge  of  5  to  35  tons, 
respectively,  and  the  metal  is  tapped  as  soon  thereafter  as  it  is  of 
the  proper  composition  and  sufficiently  hot.  The  composition  is 
determined  by  taking  a  test  ladleful  from  the  bath,  casting  it  into 
a  mold,  and  examining  a  freshly  broken  fracture,  to  determine 
either  the  amount  of  combined  and  graphitic  carbon,  or  the  depth 
of  chill,  or  both.  American  furnaces  usually  vary  in  size  from  10 
to  45  tons  capacity  each.  The  loss  will  be  about  2  to  5  per  cent, 
of  the  weight  of  metal  used. 

Lining.  —  The  lining  of  the  bottom  of  the  air-furnace  is 
made  of  silica  sand  of  about  the  same  composition  as  the  acid 
open-hearth  furnace,  i.e.,  containing  95  per  cent,  or  more  of 
silica,  with  just  enough  lime  to  frit  the  mass  together  at  the  heat 
of  the  furnace.  A  layer  about  1  to  2  in.  thick  is  spread  all  over 
the  hearth  and  then  set  on  as  described  in  the  chapter  dealing 
with  the  open-hearth  process.  About  five  layers  are  put  on 
in  this  way,  and  the  bottom  lasts  on  an  average  of  6  to  12  heats, 
although  some  foundries  regularly  make  up  a  bottom  after  the 
third  heat;  and  in  other  cases  the  bottoms  last  as  many  as  30 
heats.  Longer  life  will  be  obtained  if  the  material  is  charged 
carefully  so  as  not  to  break  the  sand,  and  if  a  strongly  reducing 
flame  is  maintained  during  the  melting  period,  when  there  is 
not  a  bath  of  liquid  iron  to  protect  the  bottom  from  the  corrosive 
iron  oxide.  Mixing  broken  fire-bricks  of  good  quality  and  re- 
fractoriness with  the  sand  seems  to  give  more  durable  bottoms. 

Scrap  Used  in  Air-Furnace.  —  Cast-iron  scrap  is  very  liable 
to  be  high  in  phosphorus  and  sulphur  and  to  vary  greatly  and  un- 
suspectedly  in  all  impurities.  Also  it  is  difficult  to  sample  for 
chemical  analysis  and  therefore  presents  some  uncertainty. 
As  the  chief  objects  of  foundrymen  in  undergoing  the  additional 
expense  of  air-furnace  melting  are  to  obtain  low  sulphur  or  a  close 
approximation  to  a  desired  analysis  or  both,  very  little  iron  scrap 
is  used.  Steel  or  wrought  iron  scrap  is  sometimes  used,  however, 
because  it  reduces  the  total  carbon  and  the  impurities  are  always 
pretty  low.  I  estimate  the  average  amount  as  between  0  and 
10  per  cent. 

Open-Hearth  Furnaces.  —  Open-hearth  furnaces  of  small  size, 
but  in  other  respects  exactly  like  the  open-hearth  steel  furnaces, 


286  THE  METALLURGY  OF   IRON  AND  STEEL 

are  used  for  melting  iron  for  malleable  castings  in  a  few  important 
foundries  in  the  United  States.  The  great  drawback  of  this  fur- 
nace is  that  it  must  be  operated  continuously,  day  and  night, 
which  means  more  floor  space  on  which  to  set  molds  ready  for 
pouring,  because  molding  cannot  well  be  done  during  the  night,  as 
the  artificial  light  casts  shadows  that  make  the  work  of  finishing 
up  molds  more  difficult  and  confusing. 

The  advantage  of  the  regenerative  open-hearth  furnace  over 
the  air-furnace  is  better  control  of  the  operation,  and  especially 
of  the  temperature,  and  greater  fuel  economy.  Figures  are  not 
given  out  by  the  companies  using  the  process,  but  we  cannot  be 
far  wrong  in  estimating  that  the  average  time  of  melting  in  the 
open-hearth  furnace  will  probably  be  somewhat  less  than  four 
hours,  and  the  amount  of  fuel  not  more  than  300  to  350  pounds 
per  ton  of  iron,  or  twice  as  much  if  melting  only  on  the  day  turn. 
The  lining  will  certainly  last  much  longer  on  account  of  the  better 
control  of  the  character  of  flame.  Moreover,  oil  can  be  used  for 
melting  in  a  regenerative  furnace,  because  it  is  introduced  into  a 
very  hot  atmosphere,  which  is  not  practicable  in  the  air-furnace, 
since  the  fuel  condenses  in  the  cooler  atmosphere  of  this  furnace, 
especially  when  the  furnace  is  cold  or  when  there  is  a  cold  charge 
on  the  hearth.  Open-hearth  linings  are  best  made  of  dolomite, 
which  enables  a  basic  slag  to  be  produced  in  the  furnace  and  a 
reduction  in  phosphorus  and  sulphur.  Cheaper  pig  iron  and  iron 
scrap  can  then  be  used.  This  basic  lining  is  not  attacked  by  the 
iron  oxide  and  slag  produced  in  melting  and  will  last  for  hundreds 
of  heats  if  not  allowed  to  cool  off  too  frequently.  Basic  linings 
cannot  be  employed  in  air-furnaces  because  dolomite  contracts 
and  expands  so  much  on  cooling  and  heating  that  the  bottoms 
are  soon  cracked  to  pieces,  for  air-furnaces  are  not  operated  con- 
tinuously. 

MELTING  STEEL  FOR  CASTINGS 

Steel  castings  are  made  in  (1)  acid  open-hearth  furnaces,  (2) 
basic  open-hearth  furnaces,  (3)  small  Bessemer  converters  of 
special  design,  to  produce  steel  at  a  higher  temperature,  and  (4) 
crucibles.  The  castings  are  made  from  the  metal  just  as  it  comes 
from  the  steel  furnace,  and  the  processes  are  mentioned  above  in 
the  order  of  relative  importance. 

Open-Hearth  Furnaces.  —  The  making  of  steel  for  castings  is 


IRON  AND   STEEL  FOUNDING  287 

practically  the  same  as  making  steel  for  ingots,  except  that  foundry 
furnaces  are  of  smaller  size,  varying  on  the  average  from  15  to  30 
tons.  In  some  cases  furnaces  smaller  than  this  are  used,  but  it  is 
generally  believed  that  no  circumstances  warrant  this,  since  the 
expense  of  running  the  small  furnaces  is  large  in  proportion. 
The  chief  difference  in  practice  is  that  the  temperature  for  steel- 
casting  work  is  hotter  than  when  ingots  are  made.  Therefore 
furnace  repairs  are  higher  and  the  life  shorter.  In  ordinary  open- 
hearth  foundry  work  the  purification  is  continued  to  the  point 
where  the  steel  contains  about  0.18  to  0.28  per  cent,  carbon  after 
recarburizing,  while  the  silicon  will  be  usually  0.20  to  0.30  per 
cent. 

Acid  versus  Basic  Open-Hearth  Steel.  —  In  steel  castings  it  is 
necessary  to  have  somewhat  lower  phosphorus  and  sulphur  than  in 
ingots,  because  the  metal  is  not  to  receive  the  beneficial  effect  of 
mechanical  work,  and  therefore  must  be  purer  in  order  to  have  a 
good  degree  of  strength  and  ductility.  Consequently,  if  we  use 
an  acid  steel-making  process,  we  must  start  with  very  low  phos- 
phorus and  low  sulphur  pig  iron,  which  is  costly  and  becomes  more 
so  each  year  in  America.  For  this  reason  the  Bessemer  and  the 
acid  open-hearth  steel-making  processes  are  more  expensive  for 
casting  work  than  the  basic  open-hearth.  The  result  is  a  present 
rapid  increase  in  the  use  of  basic  open-hearth  steel  in  America  as 
well  as  in  Germany,  with  a  probability  that  in  a  few  years  it  will 
be  the  predominant  process  for  this  purpose.  This  is  in  spite  of 
the  fact  that  basic  steel  has  very  serious  disadvantages,  chief 
among  which  are  the  amount  of  oxygen  contained  in  it  at  the  end 
of  the  process  and  the  difficulty  of  getting  the  desired  amount  of 
silicon  in  it  with  the  recarburizer,  both  of  which  conditions  in- 
crease the  liability  to  blow-holes,  which  are  especially  objection- 
able in  castings,  as  there  is  no  opportunity  of  their  being  welded  up 
and  as  castings  may  have  to  be  discarded  on  account  of  them  after 
a  good  deal  of  expensive  machine-work  has  been  done.  On  this 
account  the  acid  open-hearth  process  has  long  held  the  predomi- 
nant position  in  the  steel-casting  industry.  In  fact,  this  is  the 
only  place  where  the  acid  open-hearth  process  now  finds  important 
employment. 

Bessemer  versus  Open-Hearth.  —  The  open-hearth  furnace 
gives  a  large  amount  of  steel  at  long  intervals,  which  is  very  incon- 
venient for  foundry  work,  because  the  molds  necessary  to  take  all 


288  THE  METALLURGY  OF  IRON  AND   STEEL 

the  metal  must  be  stored  upon  the  foundry  floor  until  the  heat  is 
ready  to  pour,  and  then  those  who  are  to  do  the  teeming  must 
interrupt  their  other  work  for  half  an  hour  or  more  for  this  pur- 
pose. Even  where  the  foundry  is  large  enough  to  have  many 
furnaces,  there  is  no  surety  that  they  will  come  out  at  regular  and 
short  intervals,  because  the  operation  in  one  may  be  delayed. 
Another  disadvantage  of  the  open-hearth  process  is  that,  in  order 
to  be  economical,  it  must  be  operated  continuously  day  and  night, 
which  also  is  inconvenient  for  foundry  work.  Further,  it  is  not 
possible  to  get  the  metal  as  hot  as  desired  without  great  damage 
to  the  furnace,  which  is  subjected  to  a  higher  temperature  than 
the  metal.  Lastly,  since  hot  metal  is  desirable  for  all  castings 
except  those  of  very  large  size,  it  is  usually  necessary  to  tap  all  the 
metal  from  the  furnace  at  once,  and  recarburize  it  at  once,  which 
prevents  castings  of  special  analysis  being  made,  unless  ordered 
in  very  large  quantities.  Nowadays,  a  great  many  nickel-steel 
castings  are  made  in  open-hearth  furnaces,  but  this  requires  nice 
calculations,  so  that  the  castings  molded  shall  be  just  equal  to  the 
capacity  of  the  heat,  and  usually  results  in  a  certain  amount  of 
scrapping  of  high-class  material. 

All  these  objections  are  avoided  in  making  castings  in  Besse- 
mer converters,  but  they  too  have  their  great  disadvantages,  chief 
among  which  are  the  slight  inferiority  of  the  Bessemer  steel  and  its 
greater  cost.  The  latter  is  true  only  as  compared  with  basic  open- 
hearth  steel  (not  acid),  and  is  due  principally  to  the  amount  of 
waste  in  the  side-blown  converters  used  for  this  purpose,  and  the 
greater  cost  of  the  pig  iron  used,  which  must  be  low  in  phosphorus 
and  sulphur.  Small  converter  plants  are  so  very  cheap  —  costing 
less  than  $5000  for  apparatus  —  that  a  great  many  iron-foundries 
in  the  United  States  are  putting  them  in  as  an  adjunct  to  their 
cupola  process,  in  order  that  they  may  be  able  to  make  steel  cast- 
ings at  will.  The  amount  of  capital  tied  up  is  so  small,  and  there 
being  no  important  expense  in  starting  and  stopping  the  converter 
as  often  as  desired,  they  can  do  this  economically. 

Tropenas  Converter.  —  The  largest  number  of  converters  for 
steel-casting  work  are  of  the  Tropenas  type,  in  which  the  wind  en- 
ters the  vessel  from  seven  tuyeres  on  the  side,  and  the  converter 
is  tipped  in  such  a  manner  that  the  streams  of  air  are  deflected 
onto  the  top  of  the  bath.  The  impurities  are  oxidized  as  in  the 
regular  Bessemer  process,  except  that  the  action  is  not  quite 


IRON  AND   STEEL  FOUNDING 


289 


so  rapid,  and  the  carbon  is  burned  to  carbon  dioxide  instead  of 
carbon  monoxide,  which  generates  a  much  larger  amount  of  heat: 

C  +     O  =  CO    (generates  29,160  calories). 
C  +  2O  =  CO2  (        "         97,200       "      ). 

In  order  to  assist  in  the  superoxidation,  there  is  a  second  row 
of  tuyeres  above  the  first,  connected  with  a  separate  wind-box. 
The  wind  is  not  turned  onto  these  upper  tuyeres  until  the  carbon 
begins  to  burn.  The  pig  iron  used  for  these  converters  runs  fre- 
quently above  2  per  cent,  of  silicon,  and  this,  together  with  the 
formation  of  carbon  dioxide,  results  in  very  hot  and  fluid  steel, 
which  can  be  poured  into  castings  of  almost  any  small  size.  The 
blows  usually  last  about  15  to  20  min- 
utes, and  the  loss  is  from  17  to  20  per 
cent,  of  the  weight  of  pig  iron  charged 
into  the  cupola  in  which  it  is  melted. 
The  vessel  can  be  started  up  and  stopped 
with  very  little  expense,  and  this  ad- 
vantage over  the  open-hearth,  together 
with  the  small  amount  of  capital  nec- 
essary to  build  the  converter  plant  and 
the  other  conditions  already  mentioned, 
has  caused  about  20  of  these  conver- 
ters to  be  installed  in  America,  and 
several  in  France,  England  and  other 
countries. 

The  great  disadvantages  of  the  Tro- 
penas  converter  are  the  waste  and  the 
cost  for  making  repairs.  Slight  patch- 
ing can  be  done  through  the  mouth, 
but  there  is  a  hole  in  the  front  of  the 
converter  shell,  closed  by  a  movable  steel 
plate,  through  which  the  operator  can 
dig  his  way  into  the  interior  to  perform 
the  necessary  repairs.  As  the  lining  in 

the  neighborhood  of  the  tuyeres  is  usually  worn  out  in  less  than 
twenty  blows,  this  costly  method  of  lining  is  a  serious  drawback. 

Long-Tuyere  Converter.  —  Next  to  the  Tropenas,  the  greater 
number  of  converters  at  work  in  America  are  of  the  Long-Tuyere, 
or  Stoughton,  type,  devised  by  the  writer.  The  bottom  part  of 


FIG.  233.  —  SECTIONS  OF 
LONG-TUYERE  CON- 
VERTER. 


290  THE   METALLURGY  OF   IRON  AND  STEEL 

this  vessel  is  attached  to  the  trunnion-ring  by  a  method  similar 
to  that  used  for  regular  Bessemer  bottoms,  and  may  be  removed 
with  great  ease,  thus  cheapening  and  facilitating  repairs.  More- 
over, the  chief  repairs  are  in  the  bottom  part  at  the  mouths  of  the 
tuyeres,  and  therefore  the  lining  of  the  upper  part  does  not  have 
to  be  relined  completely  for  several  months,  although  slight  patch- 
ing is  necessary  every  twenty-five  to  thirty  blows,  when  the  bottom 
is  changed.  This  converter  is  arranged  to  have  but  one  row  of 
tuyeres,  discharging  the  blast  immediately  at  the  surface  of  the 
metal,  and  the  lining  on  the  tuyere  side  is  thicker  in  order  that  the 
tuyeres  maybe  increased  in  length, which  decreases  the  loss  of  metal 
during  the  process.  The  excessive  loss  in  the  side-blown  converters 
is  due  chiefly  to  the  spitting,  which  is  very  large,  especially  when 
the  tuyeres  have  become  worn  away  to  a  short  length  and  the 
streams  of  air  are  badly  directed  and  set  up  interfering  currents. 

Another  cause  of  the  Excessive  loss  is  the  large  amount  of  slag 
formed,  because  more  iron  is  oxidized,  and  this  corrodes  the  lining 
very  rapidly.  Part  of  the  iron  is  oxidized  at  the  mouths  of  the 
tuyeres,  and  another  part  is  oxidized  when  the  violent  agitation 
of  the  bath,  which  occurs  in  all  of  these  converters,  especially  dur- 
ing the  boil,  throws  the  metal  up  into  the  stack,  where  it  meets 
free  oxygen.  For  this  reason  the  upper  row  of  tuyeres  in  the 
Tropenas  converter  results  in  an  increase  in  the  loss  and  in  the  cor- 
rosion of  the  vessel  lining.  After  many  experiments  with  the 
Tropenas  vessel,  I  learned  that  the  maximum  amount  of  carbon 
can  be  oxidized  to  CC>2  without  the  use  of  the  upper  row  of  tuyeres, 
and  therefore  economy  could  be  obtained  by  omitting  them.  In 
fact,  at  some  Tropenas  plants  the  valve  of  the  upper  row  of  tuyeres 
is  often  not  opened  at  all  during  the  heat,  and  no  diminution  of 
the  temperature  of  the  resulting  steel  is  observed.  The  loss  in  the 
Long-Tuyere  modification  is  14  to  16  per  cent.,  including  cupola 
loss. 

Sizes  Used.  —  Most  of  the  small  converters  have  a  capacity  of 
about  2  tons,  because  this  is  economical  and  well  proportioned  to 
the  capacity  of  an  ordinary  foundry.  There  are  some  4-  and  5-ton 
converters,  however,  and  some  of  less  than  1  ton  capacity.  Sizes 
less  than  2  tons  are  very  costly  to  operate  in  proportion  to  their 
output.  The  blast  pressure  usually  employed  is  3  to  5  lb.,  with  an 
average  of  about  3f  lb. 


IRON  AND   STEEL  FOUNDING 


291 


TABLE  XXIL— ANALYSES  OF  SIDE-BLOWN  CONVERTER-GASES 


ANALYSES  —  PER  CENT. 

CALCULATIONS  FROM 
ANALYSES  —  PER  CENT. 

o 

D 

TIME  AFTER  BEGINNING 

M  01 

a 

OF  BLOW 

1 

CO 

CO2 

O 

N 

and 
H 

Total 
0 

N» 

O 
Enter- 
ing 

3  fl'rt 

PQ  *  a 

1 

4  min.,  flame  starts.  .  . 

0.0 

8.2 

1.1 

90.7 

7.1 

88.7 

23.6 

16.5 

2 

10     "     boiling  

0.3 

24  3 

0.4 

75.0 

18.3 

73.0 

19.4 

1.1 

3 

12     "      shortening2.... 

0.4 

8.8 

0.2 

90.6 

6.8 

88.6 

23.5 

16.7 

4 

17     "      after  first  drop. 

10.7 

13.0 

0.2 

76.1 

15.8 

74.1 

19.7 

3.9 

21      "     end  of  blow... 

1  By  difference,  H  being  estimated  as  2  per  cent. 

2  I.e.,  just  before  the  first  drop.     There  are  two  drops  to  the  flame  in  this 
operation,  the  second  marking  the  end. 


91 


92. 


REFERENCES  ON  FOUNDRY  PRACTICE 

90.  George  R.  Bale.  "Modern  Iron  Foundry  Practice."  Part  I. 
Foundry  Equipment,  Materials  Used,  and  Processes  Fol- 
lowed. 1902.  Part  II.  Machine  Molding  and  Molding 
Machines,  Physical  Tests  of  Cast  Iron,  Methods  of  Cleaning 
Castings,  Foundry  Accounting,  etc.,  etc.  1905.  London. 
This  is  the  most  scientific  book  on  iron  foundry  practice 
published. 

The  Foundry.  Published  monthly.  Vol.  xxxi,  1907.  Cleve- 
land, Ohio. 

Thomas  D.  West.  "American  Foundry  Practice."  Treating 
of  Loam,  Dry-Sand  and  Green-Sand  Molding,  and  con- 
taining a  Practical  Treatise  upon  the  Management  of 
Cupolas  and  the  Melting  of  Iron.  Published  in  New  York. 
This  book  is  tremendously  popular  among  foundry  men  and 
editions  appear  at  frequent  intervals. 

William  J.  Keep.  "Cast  Iron."  A  Record  of  Original  Re- 
search. New  York  and  London,  1902. 

Thomas  Turner.  "  Lectures  on  Iron-Founding."  London,  1904. 

"Penton's  Foundry  List."  Cleveland,  Ohio,  1906.  A  Direc- 
tory of  the  Foundries  of  the  United  States  and  Canada. 

For  an  account  of  small  converters  for  steel  casting  work  see 
Reference  No.  52  and  the  files  of  Nos.  91  and  8. 


93 

94 
95 


THE  SOLUTION  THEORY  OF  IRON  AND   STEEL 

SCIENTIFICALLY  considered,  all  of  the  members  of  the  iron  and 
steel  series  are  alloys  of  iron  and  carbon.  Therefore  a  study  of 
the  general  theory  of  alloys  leads  to  important  information  upon 
iron  and  steel.  According  to  the  authoritative  definition,  "a 
metallic  alloy  is  a  substance  possessing  the  general  physical 
properties  of  a  metal,  but  consisting  of  two  or  more  metals,  or  of 
metals  with  non-metallic  bodies,  in  intimate  mixture,  solution,  or 
combination  with  one  another,  forming,  when  melted,  a  homo- 
geneous fluid."  It  will  be  seen  from  this  that  the  essential  feature 
of  an  alloy  is  that,  when  melted,  it  shall  form  a  homogeneous  fluid. 
In  plain  language,  this  means  that,  when  melted,  the  different 
components  are  dissolved  in  one  another.  Melted  alloys,  there- 
fore, come  under  the  general  head  of  solutions.  In  fact,  the 
great  bulk  of  our  alloys,  and  especially  of  iron  and  steel,  are  pro- 
duced by  first  dissolving  the  melted  components  and  then  allowing 
them  to  freeze.  The  laws  governing  this  freezing,  or  solidification, 
have  only  been  known  a  few  years,  and  if  this  new  knowledge  has 
made  great  revolutions  in  physical  chemistry,  it  has  led  to  no  less 
important  discoveries  in  regard  to  the  nature  of  iron  and  steel. 

Solid  Solutions.  —  Suppose  first  we  have  two  metals  that  are 
soluble  in  each  other  when  liquid,  and  also  when  solid.  In  other 
words,  the  metals  of  the  alloy  will  be  just  as  completely  dissolved 
in  each  other  after  solidification  as  before.  They  will  then  form  a 
"solid  solution,"  and  a  solid  solution  bears  practically  the  same 
relation  to  a  liquid  solution  as  a  solid  pure  metal  does  to  the  same 
metal  when  liquid.  For  example,  gold  and  silver  dissolve  in  each 
other  when  liquid,  and  also  when  solid,  in  any  proportion.  Con- 
sequently any  solution  of  these  metals  will  cool  to  the  freezing- 
point  and  then  solidify  without  there  being  any  important  change 
(from  the  metallurgical  or  practical  standpoint)  in  the  relations  of 
the  two  metals  after  the  freezing.  The  reason  that  these  solid 

292 


THE   SOLUTION  THEORY   OF   IRON  AND   STEEL         293 

solutions  form  in  any  proportion  is  that  the  two  metals  crystallize 
alike.  It  is,  perhaps,  a  new  thought  to  the  reader,  but  it  is  never- 
theless true,  that  a  metal  forms  a  crystal  whenever  it  solidifies. 
Furthermore,  each  metal  has  a  particular,  general  shape  which  its 
crystals  assume,  and  there  is  almost  no  force  powerful  enough  to 
prevent  them  from  taking  that  same  shape  in  preference  to  any 
other. 

Tiny  as  the  crystals  sometimes  are — often  requiring  the  highest 
powers  of  the  microscope  to  reveal  them  —  their  crystalline  forces 
are  very  powerful.  If,  therefore,  two  metals  do  not  form  like  crys- 
tals, they  cannot  solidify  in  solution,  i.e.,  in  the  same  crystal,  but 
crystallization  (i.e.,  freezing)  must  be  accompanied  by  precipita- 
tion. 

By  European  metallurgists  solid  solutions  are  often  called 
"mixed  crystals,"  or  "isomorphous  mixtures/7  but  this  termi- 
nology is  objected  to  because  the  relation  of  two  substances  when 
dissolved  is  far  more  intimate  than  any  mixture  possibly  could  be. 
In  a  mixture,  the  microscope  will  always  be  powerful  enough  to 
distinguish  the  different  components,  but  a  solution  always  appears 
like  a  simple  uniform  body.  Furthermore,  the  properties  of  a  mix- 
ture are  intermediate  between  the  properties  of  its  components, 
but  a  solution  —  either  liquid  or  solid  —  has  some  properties 
which  are  different  from  any  of  the  properties  of  either  of  its  com- 
ponents. Again,  the  components  of  a  solution  are  held  together 
by  chemical  forces,  while  the  components  of  a  mixture  are  either 
not  held  together  at  all,  or  only  because  of  close  mechanical  asso- 
ciation. In  brief,  a  solution  has  some  of  the  peculiarities  of  a 
chemical  compound,  and  differs  from  such  a  compound  chiefly 
because  the  latter  must  always  be  composed  of  definite  amounts 
of  each  component,  and  in  some  multiple  of  their  atomic  weights, 
while  a  solution  may  contain  widely  varying  amounts  of  each 
component. 

Freezing  of  Solid  Solutions.  —  When  metals  form  solid  solu- 
tions, the  solutions  freeze  more  or  less  like  pure  metals.  In  Fig.  234 
I  have  shown  graphically  the  freezing  of  all  the  alloys  of  gold  and 
silver,  extending  from  no  silver  (i.e.,  100  per  cent,  gold)  to  no  gold 
(100  per  cent,  silver).  This  figure  has  been  drawn  from  results 
obtained  by  experiment.  The  proportion  of  silver  is  shown  by 
the  abscissae,  or  the  horizontal  distance  away  from  the  axis  OC, 
and  the  temperature  is  shown  by  the  ordinates,  or  the  vertical 


294 


THE  METALLURGY  OF   IRON  AND   STEEL 


distance  away  from  the  axis  00.  In  other  words,  any  point 
between  these  two  axes  represents  by  one  ordinate  the  composi- 
tion of  the  alloy  in  silver,  and  by  the  other  ordinate  the  tempera- 
ture at  which  the  alloy  is  at  the  moment.  For  example,  the  point 
marked  a  is  a  certain  distance  from  the  axis  0  C,  which  shows  that 
the  alloy  in  question  contains  50  per  cent,  of  silver;  it  is  also  a  cer- 
tain distance  above  the  axis  00,  which  shows  that  the  alloy  is 
now  at  a  temperature  of  1100°  C.  (1012°  F.). 

Since  there  is  nothing  in  the  alloys  but  silver  and  gold,  the 
amount  of  gold  in  each  will  be  the  complement  of  the  amount  of 


1200C 


noo 


2192  F 


900 


0          10*  Silver 
100  H  Gold 


FIG.  234.  — FREEZING  CURVE  OF  THE  GOLD-SILVER  ALLOYS. 

silver.  That  is  to  say,  the  percentage  of  silver  plus  the  percentage 
of  gold  must  always  equal  100  per  cent. ;  if  there  is  25  per  cent,  of 
silver  there  must  be  75  per  cent,  of  gold;  if  there  is  50  per  cent,  of 
silver  there  must  be  50  per  cent,  of  gold,  etc.  The  horizontal  dis- 
tances therefore  show  the  percentage  of  gold  as  well  as  of  silver, 
and  this  is  given  in  the  second  line  of  figures  under  the  table. 

Suppose  we  have  a  solution  of  50  per  cent,  silver  and  50  per 
cent,  gold  at  a  temperature  of  1100°  C.  It  is  represented  at  the 
point  a,  and  is  now  liquid.  When  it  cools  to  about  1035°  C.  it  begins 
to  freeze.  It  does  not  all  freeze  at  the  same  time,  but  first  some 
solid  crystals  freeze  out  and  we  have  a  mixture  of  solid  crystals 
with  liquid  solution.  The  more  the  mass  cools  the  more  solid 
crystals  there  will  be,  each  crystal  being  a  solid  solution  of  gold 
and  silver.  It  is  not  until  we  reach  a  temperature  of  985°  C.,  how- 
ever, that  the  last  liquid  freezes,  and  then  we  have  a  solid  solution 
of  gold  and  silver,  the  two  solid  metals  now  bearing  practically 
the  same  relation  to  each  other  chemically  that  they  did  when 
liquid. 

It  will  be  noticed  that  when  this  alloy  cooled  from  the  point  a 


THE  SOLUTION  THEORY  OF   IRON  AND   STEEL         295 

to  1035°,  it  met  the  line  A  E  B.  This  is  the  line  that  represents  the 
beginning  of  freezing  for  all  the  gold-silver  alloys.  It  has  been 
drawn  after  many  experiments  have  been  made  to  show  where  it 
lies  in  the  diagram.  It  will  furthermore  be  noticed  that  when  this 
alloy  cooled  to  985°,  it  met  the  line  ADB.  This  is  the  line  that 
represents  the  completion  of  freezing  for  all  the  gold-silver  alloys, 
and  its  position  has  been  learned  from  many  experiments. 

Take  now  the  alloy  containing  60  per  cent,  silver  and  40  per 
cent,  gold,  at  a  temperature  of  1150°  C.  — the  point  b.  As  this 
cools  to  a  temperature  of  1025°  C.,  it  meets  the  line  AE  B  and 
freezing  begins  in  the  same  way  as  before.  Solid  crystals  form 
more  and  more  as  the  alloy  cools  further,  until  we  meet  the  line 
ADB  at  a  temperature  of  980°  C.  At  this  point  the  last  liquid 
freezes. 

THE  FREEZING  OP  ALLOYS  OF  LEAD  AND  TIN 

1.  Suppose  now,  on  the  other  hand,  we  have  two  metals  which 
are  soluble  in  each  other  when  melted,  but  not  when  solid.     Evi- 
dently there  cannot  be  the  same  results  as  those  described  in  the 
case  of  the  gold-silver  alloys.     Such  a  series  is  found  in  the  alloys 
of  lead  and  tin,  whose  freezing  is  shown  graphically  in  Fig.  235. 
Here  again  I  have  shown  the  percentage  of  lead  and  tin  by  the 
horizontal  ordinates,  and  the  temperature  by  the  vertical  ordi- 
nates.     And,  again,  the  diagram  has  been  drawn  from  results  ob- 
tained by  experiment.     The  following  facts  are  not  based  upon 
reasoning  or  logic,  but  are  to  be  accepted  because  it  is  known  that 
the  different  actions  described  actually  took  place  upon  trial. 

2.  Consider  first  a  solution  containing  83  per  cent,  of  lead  and 
at  a  temperature  of  300°  C.     This  will  be  represented  by  the  point 
a  in  Fig.  235  (page  299),  and  will  be  a  solution  of  lead  in  tin,  still 
liquid,  although  about  26°  below  the  melting-point  of  lead  itself. 
If  cooled,  the  solution  will  remain  liquid  until  it  reaches  a  tem- 
perature of  about  275°,  which  brings  it,  we  see,  to  the  line  A  B. 
This  is  the  lowest  temperature  to  which  it  will  go  and  retain  that 
much  lead  in  solution.     If  cooled  any  more,  the  lead  will  begin  to 
precipitate  and  of  course  as  much  as  is  precipitated  will  immedi- 
ately solidify,  being  already  well  below  its  melting-point.     The 
lead  comes  out  as  crystals  of  solid  lead,  which  remain  mixed  with 
the  mass  of  the  molten  solution,  but  form  no  longer  a  part  of  it 


296  THE  METALLURGY  OF   IRON  AND   STEEL 

chemically.1  The  solution,  i.e.,  the  part  still  liquid,  becomes  en- 
riched in  tin  in  proportion  as  the  lead  precipitates.  Leaving  this 
alloy  here  for  the  moment,  let  us  next  consider  one  with  less  lead. 

3.  Now  take  an  alloy  with  67  per  cent,  of  lead  and  33  per  cent, 
of  tin  at  a  temperature  of  250°  C.     This  will  be  represented  by  the 
point  b  in  Fig.  235.    We  have  again  liquid  lead  dissolved  in  liquid 
tin,  although  the  alloy  is  76  per  cent,  below  the  melting-point  of 
pure  lead.     Suppose  this  alloy  cools  until  it  reaches  a  tempera- 
ture of  about  240°  C.,  where  it  meets  the  line  A  B.     It  will  not  cool 
below  that  temperature  and  retain  all  the  lead  in  solution.     If  we 
cool  it  a  few  degrees,  lead  separates  out  and  becomes  mechanically 
mixed  with  the  liquid  solution. 

4.  Consider  next  an  alloy  of  55  per  cent,  lead  dissolved  in  45 
per  cent,  of  tin  at  a  temperature  of  250°  C.     As  this  cools  to  a 
temperature  slightly  below  225°,  it  again  meets  the  line  A  B  and 
crystals  of  lead  separate  out  and  solidify.     And  so  on:  any  solu- 
tion, when  it  cools  to  a  temperature  where  it  meets  the  line  A  B, 
reaches  its  limit  of  solubility ;  it  cannot  cool  m6re  and  retain  all  of 
the  lead  in  solution ;  but  if  it  does  cool,  then  some  of  the  lead  must 
be  precipitated.2 

5.  To  sum  up  the  preceding  paragraphs,  we  may  then  say  that 
the  less  lead  we  have  in  solution,3  the  lower  the  temperature  can 
go  without  any  of  it  being  precipitated.     Or,  in  other  words,  the 
less  the  lead  in  solution  the  lower  the  temperature  will  go  before 
any  freezing  begins.     This  knowledge  is  the  result  of  experiment, 
and  it  has  been  shown  that  the  line  A  B  in  Fig.  235  represents  the 
equilibrium  between  the  amounts  of  lead  in  the  different  solutions 
and  the  temperature  to  which  each  will  cool  before  any  lead  is 
precipitated,  or,  in  other  words,  the  amount  of  lead  that  saturates 
the  solution  at  each  temperature. 

1  It  is  a  fact  that  when  the  lead  is  precipitated  from  the  solution,  it  car- 
ries with  it  a  few  traces  of  dissolved  tin,  but  for  the  present  we  neglect  this 
slight  impurity  for  the  sake  of  simplicity,  and  consider  that  pure  lead  sep- 
arates. 

2  Any  lead  that  is  precipitated  must  of  course  freeze,  because  the  tem- 
perature is  already  below  the  freezing-point  of  lead.     Conversely,  any  lead 
that  freezes  must  be  precipitated  from  the  alloy,  because  we  know  as  a  matter 
of  experiment  that  frozen  lead  will  not  retain  tin  in  solution  (omitting,  of 
course,  the  few  traces  of  tin  retained  by  the  lead  and  which,  for  the  sake  of 
simplicity,  we  omit  in  the  discussion). 

•Within  limits  to  be  afterward  denned. 


THE   SOLUTION  THEORY  OF   IRON  AND   STEEL         297 

6.  With  this  knowledge  let  us  consider  again  the  first  solution 
—  containing  83  per  cent,  of  lead.     We  have  stated  that  when 
this  solution  was  cooled  below  275°  C.,  some  lead  was  precipitated. 
Have  we  any  evidence  now  as  to  how  much  lead  would  be  precipi- 
tated with  each  unit  drop  in  temperature?     Evidently  we  have, 
for  we  know  how  much  lead  is  normally  in  the  saturated  solution 
at  each  temperature ;  this  evidence  is  given  to  us  by  the  line  A  B. 
For  example,  assume  that  the  solution  containing  83  per  cent,  of 
lead  is  cooled  to  240°  C.;  how  much  lead  will  be  left  in  solution, 
and   therefore  how  much   will  have  been   precipitated?     From 
paragraph  3  we  know  that  67  per  cent,  of  lead  remained  in  solution 
down  to  a  temperature  of  240°  C.  and  that  there  was  an  equilib- 
rium between  the  amount  of  lead  and  this  temperature,  or,  in 
other  words,  the  solution  is  saturated  with  lead  at  this  point. 
Therefore  it  would  be  reasonable  to  suppose  that  the  solution 
which  started  with  83  per  cent,  of  lead  would  retain  exactly  67 
per  cent,  of  lead  by  the  time  the  temperature  of  240°  is  reached. 
That  this  reasoning  is  correct  is  proved  by  experimental  evidence. 

7.  Now  let  us  cool  the  same  alloy  to  a  temperature  of  225°; 
how  much  lead  will  this  retain  in  solution  and  how  much  would  be 
in  a  precipitated  form?     We  have  already  seen  (paragraph  4) 
that  an  alloy  containing  55  per  cent,  of  lead  will  retain  all  of  that 
lead  in  solution  until  it  falls  to  a  temperature  of  225°.     Therefore 
it  is  reasonable  to  suppose  that  the  cooling  alloy  we  are  considering 
will  retain  just  55  per  cent,  of  lead  and  no  more  by  the  time  its 
temperature  has  fallen  to  225°,  and  this  is  in  fact  the  case.     In 
short,  each  solution  will  always  retain  enough  lead  to  saturate  itself 
after  it  once  becomes  saturated. 

8.  We  have  learned  above  that  every  point  on  the  line  A  B 
represents  the  maximum  amount  of  lead  that  can  be  retained  in 
one  of  these  solutions  at  that  temperature.     Therefore  as  soon  as 
any  solution  meets  the  line  A  B,  it  follows  along  this  line  as  it  cools 
and  lead  precipitates  in  amounts  proportional  to  the  temperature, 
so  that  the  solutions  will  always  be  saturated  with  lead. 

9.  It  is  therefore  evident  that  if  we  start  with  any  of  these  liquid 
alloys  containing  an  amount  of  lead  represented  on  the  diagram 
to  the  left  of  the  point  B,  lead  will  precipitate  from  it  during  cool- 
ing and  the  amount  of  lead  in  solution  will  continually  decrease, 
so  that  the  composition  of  the  alloy  at  the  different  temperatures 
will  be  represented  by  a  point  traveling  down  the  line  A  B.    There- 


298  THE  METALLURGY  OF   IRON  AND   STEEL 

fore,  in  every  such  case  we  shall  reach  finally  a  solution  with  31 
per  cent,  of  lead  and  69  per  cent,  of  tin  (the  proportions  repre- 
sented by  the  abscissa  of  the  point  B)  when  the  temperature  has 
fallen  to  180°  C.  (the  ordinates  of  the  point  B).  Mixed  with  the 
solution  at  this  temperature  will  be  the  amount  of  lead  which  has 
separated  during  cooling  and  which  will  depend  upon  the  percentage 
in  the  original  solution.  (If  this  is  not  clear  on  the  first  reading,  a 
little  thought  will  make  it  so,  especially  if  the  reader  follows  in 
Fig.  235  each  action  I  have  described,  step  by  step.) 

10.  We  have  considered  up  to  now  only  the  solutions  con- 
taining large  amounts  of  lead  and  from  which  lead  is  precipitated 
on  cooling.     Let  us  now  consider  a  solution  containing  90  per 
cent,  of  tin  at  a  temperature  of  225°  C.  (point  d,  Fig.  235).     It  is 
still  liquid,  although  below  the  normal  melting  temperature  of 
both  lead  and  tin.     This  will  cool  until  a  temperature  of  about 
210°  is  reached  and  it  meets  the  line  C  B.     If  it  cools  any  more, 
tin  will  be  precipitated  and  will  of  course  freeze,  because  it  is 
already  below  its  normal  freezing-point  (231°  C). 

11.  Consider  next  an  alloy  containing  85  per  cent,  of  tin  at  a 
temperature  of  225°  (point  e  in  Fig.  235).     This  will  cool  to  about 
200°  C.,  where  it  meets  the  line  C  B,  but  if  it  cools  any  further,  tin 
will  be  precipitated  and  will  freeze. 

12.  In  other  words,  the  line  C  B  represents  the  conditions  of 
equilibrium  between  the  temperature  and  the  amount  of  tin  that 
will  be  retained  in  solution,  just  as  the  line  A  B  represented  the 
equilibrium  between  the  temperature  and  the  amount  of  lead  that 
would  be  retained  in  solution.     That  is  to  say,  every  point  on  the 
line  C  B  represents  the  amount  of  tin  that  will  saturate  a  solution 
at  that  temperature. 

13.  Returning  then  again  to  the  alloy  containing  90  per  cent, 
of  tin,  how  much  tin  will  have  been  precipitated  by  the  time  the 
alloy  cools  to,  let  us  say,  200°  C.?    Obviously  5  per  cent,  of  tin 
would  have  been  precipitated,  leaving  a  solution  containing  85 
per  cent,  of  tin,  because  we  have  already  seen  that  85  per  cent,  of 
tin  will  saturate  a  solution  at  200°  C. 

14.  Whatever  solution  we  may  have  had  to  start  with,  pro- 
vided there  was  always  more  than  69  per  cent,  of  tin,  as  soon  as 
that  solution  met  the  line  C  Bit  would  travel  down  this  line,  precip- 
itating tin  progressively  in  proportionate  amounts  such  that  the 
tin  left  in  the  solution  at  the  varying  temperatures  would  corre- 


THE   SOLUTION  THEORY  OF   IRON  AND   STEEL 


299 


spond  to  the  ordinates*  of  the  line  C  B.  In  other  words,  this  solu- 
tion follows  the  line  C  B.  Therefore,  in  all  such  alloys  we  shall 
finally  arrive  at  a  solution  having  31  per  cent,  of  lead  and  69  per 
cent,  of  tin  (the  abscissa  of  the  point  B)  when  the  temperature 
has  fallen  to  180°  C.,  and  with  this  solution  will  be  mixed  precipi- 
tated tin  in  amount  depending  upon  the  amount  of  tin  in  the 
original  solution.  This  solution  is  known  as  the  'eutectic'  solu- 
tion. 

15.  We  may  now  sum  up  paragraphs  9  and  14  by  saying  that 
whatever  solution  of  lead  and  tin  we  have  to  start  with,  we  will 


C.  350 


S>    200 


150 


100 


Tin        0  10 

Lead   100  90 


8C2   F. 


572 


392° 


212° 


32° 


90  100'Per-cent 

10  0     Per  cent 


FIG.  235.  — THE  FREEZING  OF  ALLOYS  OF  LEAD  AND  TIN. 


always  have  one  containing  31  per  cent,  of  lead  and  69  per  cent, 
of  tin  by  the  time  the  temperature  has  fallen  to  180°,  and  with 
this  solution  will  be  mixed  some  precipitated  tin  or  precipitated 
lead,  as  the  case  may  be  (unless,  of  course,  we  started  with  exactly 
31  per  cent,  of  lead  and  69  per  cent,  of  tin). 

Now  let  us  consider  the  further  cooling  of  these  alloys.  Evi- 
dently, no  change  will  take  place  in  the  precipitated  lead  or  tin,  as 
either  of  them  would  be  already  in  the  solid  form.  What  will 
happen,  however,  to  the  solution  containing  31  per  cent,  of  lead 
and  69  per  cent,  of  tin,  which  we  have  called  the  'eutectic'  solu- 
tion? It  is  evident  that  when  this  solution  cools  below  180°,  it 
must  cross  the  point  B,  and  therefore  both  the  lines  A  B  and  B  C 


300  THE  METALLURGY  OF   IRON  AND   STEEL 

at  once.  Obviously,  it  cannot  cross  either  of  these  lines  without 
precipitating  lead  or  tin.  In  point  of  fact,  on  crossing  both  of  the 
lines  at  the  same  time,  it  precipitates  at  once  all  the  remaining 
lead  and  all  the  remaining  tin,  and  therefore  completes  the  decom- 
position of  the  solution  and  the  solidification. 

The  lead  and  tin  separate  in  tiny  solid  crystals  or  flakelets, 
which  arrange  themselves  in  a  parallel  banded  structure  similar 
to  that  shown  in  Fig.  240,  page  313.  This  structure  is  known  as 
the  'eutectic'  structure,  after  the  alloy  which  always  results  when 
any  one  of  the  solutions  of  the  series  is  cooled.  The  term  '  eutectic 
alloy'  means  etymologically  'well-melting  alloy/ because  it  remains 
melted  longer  than  any  other  alloy  of  the  same  metals,  and  every 
solution  the  components  of  which  are  soluble  in  each  other  in  the 
liquid  state  and  insoluble  in  the  solid  state  will  form  a  eutectic 
solution  in  the  way  I  have  described.  This  applies  not  only  to 
solutions  of  metals  in  each  other,  but  to  solutions  of  metals  in 
liquids  which  are  afterward  frozen,  and  even  of  salts  in  water,  etc. 

Freezing-Point  Curves. — The  lines  A  B  and  CB  are  often 
spoken  of  as  the  "upper  freezing-point  curves"  of  the  alloys,  be- 
cause any  alloy  which  cools  to  this  line  will  then  commence, to 
freeze.  Furthermore,  freezing  once  having  commenced  when 
either  of  these  lines  is  reached,  will  continue  progressively  as 
the  excess  metal  separates  out.  The  line  D  E  is  often  called  the 
'lower  freezing-point  curve/  because  this  line  represents  the 
temperature  of  freezing  of  the  eutectic  of  the  series,  and  we  have 
already  shown  that  every  alloy  in  the  series  automatically  forms  a 
eutectic  by  'selective'  precipitation;  therefore  every  alloy  in  the 
series  will  not  be  entirely  solid  until  it  reaches  the  temperature  at 
which  the  eutectic  solidifies,1  which  is  always  the  same. 

Cooling  Curves.  —  There  are  certain  thermal  changes  which 
accompany  the  chemical  changes  I  have  outlined  in  the  preceding 
paragraphs.  These  thermal  changes  are  of  importance,  because 
it  is  by  means  of  them  that  we  are  usually  able  to  obtain  the  first 
evidence  of  the  precipitation  of  excess  metal,  the  formation  and 
solidification  of  a  eutectic,  etc.  Consider  the  alloy  containing 
83  per  cent,  of  lead  and  17  per  cent,  of  tin,  at  300°  C.,  and  let  us 
observe  by  means  of  a  thermometer  or  pyrometer  the  rate  of 

1  Some  metallurgists  prefer  not  to  draw  the  line  D  E,  but  to  represent  the 
freezing  of  the  eutectic  merely  by  the  point  B. 


THE   SOLUTION  THEORY   OF   IRON  AND  STEEL 


301 


cooling.  At  first  the  thermometer  will  fall  pretty  fast,  but  when 
we  reach  275°,  where  the  line  A  B  is  met,  the  rate  of  fall  is  suddenly 
retarded.  It  thus  becomes  evident  to  us  that  some  event  coun- 
teracts the  fall  in  temperature.  What  this  event  is  we  learn  from 
microscopic  evidence,  and,  as  has  already  been  explained,  it  is  the 
precipitation  of  lead.  This  explanation  might  have  been  ex- 
pected, because  the  precipitation  of  lead  at  a  temperature  below 
its  normal  freezing-point  would  of  course  be  accompanied  by 
freezing  and,  during  the  freezing,  the  metal  would  liberate  its 
latent  heat  of  fusion  and  thus  oppose  the  cooling  of  the  mass  as  a 


300C 


100 


b    Eutectic 


freezing 


572  F 


212° 


10  Minutes 


20  Minutes 


FIG.  236.  —  FREEZING  CURVE  OF  AN  ALLOY  CONTAINING  83  PER  CENT. 
OF  LEAD   AND    17   PER   CENT.    OF   TIN. 


whole.  The  rate  of  fall  of  temperature  is,  moreover,  retarded  all 
the  way  down  to  180°,  because  lead  is  being  continuously  precipi- 
tated as  the  solution  travels  down  the  line  A  B.  When  we  reach 
180°,  the  fall  of  temperature  is  not  only  retarded  but  actually 
ceases;  in  some  cases  the  temperature  may  rise  slightly.  This 
change  is  due  to  the  large  amount  of  latent  heat  of  fusion  liberated 
by  the  freezing  of  the  eutectic.  This  arrest  continues  until  the 
eutectic  is  entirely  solid,  after  which  the  rate  of  fall  becomes  rapid 
again  and  proceeds  without  important  change  until  the  atmos- 
pheric temperature  is  reached,  because  now  we  have  merely  the 
cooling  of  a  solid  alloy. 

These  changes  are  represented  diagrammatically  in  Fig.  236, 
in  which  the  abscissae  show  the  time,  in  minutes,  from  the  begin- 


302  THE  METALLURGY  OF   IRON  AND   STEEL 

ning  of  the  cooling,  and  the  ordinates  show  temperatures.  The 
change  in  direction  at  the  point  a  shows  the  retardation  due  to 
the  precipitation  of  the  lead,  while  the  long  horizontal  part  at  b 
shows  that  for  several  minutes  the  temperature  was  not  falling 
at  all,  because  the  eutectic  was  freezing. 

Next,  experimenting  upon  the  alloy  with  67  per  cent,  of  lead, 
we  find  that  it  cools  rapidly  until  it  meets  the  line  A  B,  when  the 
rate  of  fall  is  retarded  continuously  until  we  reach  180°,  where 
again  an  arrest  (or  perhaps  an  actual  rise)  of  the  temperature  is 
observed,  after  the  completion  of  which  the  fall  in  temperature 
becomes  rapid  again  and  proceeds  normally. 

Similar  thermal  changes  are  observed  in  the  alloy  containing 
55  per  cent,  of  lead,  but  at  temperatures  of  225°  and  180°.  Now, 
by  plotting  the  upper  changes  in  the  several  solutions  (i.e.,  at 
275°  C.,  at  240°  C.,  and  at  225°  C.),  the  position  of  the  line  A  B  is 
determined,  and  by  plotting  the  lower  changes  (i.e.,  at  180°  C.  in 
each  case)  the  line  D  E  is  determined. 

In  studying  the  solutions  of  the  series  rich  in  tin,  similar 
thermal  changes  are  observed.  Consider  the  alloy  containing 
90  per  cent,  of  tin  and  10  per  cent,  of  lead;  this  will  cool  rapidly 
until  a  temperature  of  210°  C.  is  reached,  when  a  retardation  will 
occur  and  will  persist  until  the  temperature  180°  is  reached.  By 
this  time  the  excess  tin  will  all  have  been  precipitated  and  the 
residual  solution  1  will  have  travelled  down  the  line  C  B  to  the 
point  B.  Thereupon  an  arrest  (for  an  actual  reversal)  in  the  rate 
of  cooling  will  occur  until  the  eutectic  has  solidified,  after  which 
the  cooling  will  proceed  at  a  rapid  rate.  In  the  case  of  the  alloy 
containing  85  per  cent,  of  tin,  the  first  retardation  will  begin  at 
200°,  and  then  an  arrest  at  180°.  By  plotting  the  points  at  210° 
and  200°,  we  obtain  the  position  of  the  line  C  B  2,  and  by  plotting 
the  two  points  at  180°  we  obtain  further  points  to  determine  the 
line  D  E. 

Properties  of  Eutectics.  —  As  already  said,  not  only  the  lead- 

1  These  residual   solutions  are   technically  known  as  '  mother  liquors '  or 
'mother  metals,'  because  it  is  out  of  them  that  the   solid  metal  is  being 
'born/ 

2  It  should  be  understood  that  in  actual  experimental  determination  of  lines 
corresponding  to  A  B,  C  B  and  D  E,  in  any  series  of  alloys,  not  a  few,  but  a 
large  number  of  different  solutions  are  studied,  and  a  great  many  retardation 
points  are  found  before  the  lines  are  drawn. 


THE   SOLUTION  THEORY  OF   IRON  AND   STEEL 


303 


tin  alloys,  but  every  alloy  of  which  the  components  are  soluble 
when  liquid,  and  insoluble  (or  nearly  so)  when  solid,  will  form 
eutectics,  and  it  happens  that  this  is  the  case  with  the  great 
majority  of  our  metallic  alloys.  For  this  reason  the  properties 
of  the  eutectic  are  very  important  in  all  metallurgical  work.  It 
will  be  seen  that  a  eutectic  is  not  a  chemical  compound  in  atomic 
proportions.  For  example,  in  the  case  of  the  lead-tin  alloys,  the 
point  B  comes  at  31  per  cent,  of  lead  and  69  per  cent,  of  tin  merely 


10 

Lead  100         90 


90      100  Per- 
ID         0  Cent 


FIG.   237.  —  FREEZING-POINT  AND   STRENGTH   CURVE   OF  THE   LEAD-TIN 

ALLOYS. 

because  the  line  A  B  crosses  the  line  C  B  at  this  ordinate,  and  this 
has  no  relation  to  atomic  ratios.  If  the  melting-point  of  tin  hap- 
pened to  be  higher,  or  if  it  did  not  precipitate  from  lead  so  fast 
upon  cooling,  the  line  C  B  would  cut  the  line  A  B  at  a  different 
point,  and  therefore  the  composition  of  the  eutectic  would  be 
different. 

The  structure  also  of  the  eutectic  is  very  important.     The 
majority  of  eutectics  have  a  structure  similar  to  the  banded  form 


304  THE   METALLURGY   OF   IRON  AND   STEEL 

shown  in  Fig.  240.  The  tiny  crystals  in  this  structure  are  inter- 
mingled very  intimately,  and  this  close  association  has  a  bene- 
ficial effect  on  the  strength  of  the  mixture.  In  Fig.  237  we  may 
see  how  the  curve  showing  tensile  strength  rises  to  a  maximum 
at  the  point  corresponding  to  the  eutectic  of  the  series  of  lead-tin 
alloys. 

THE  FREEZING  OF  IRON  AND  STEEL 

1.  When  the  iron  and  steel  alloys  are  liquid,  they  are  com- 
posed of  liquid  carbon  dissolved  in  liquid  iron,  and  their  freezing- 
point  curves  are  shown  in  Fig.  238.     It  will  be  noticed  that  the 
lines  in  this  figure  bear  a  close  similarity  to  those  in  Fig.  235.    This 
similarity  is  real,  and  the  laws  governing  the  freezing  of  this  series 
of  alloys  are  very  similar  to  those  governing  the  freezing  of  the 
lead-tin  alloys.     There  is  a  eutectic  of  this  series  when  the  line 
A  B  crosses  the  line  C  B,  and  the  components  of  this  eutectic  are 
95.7  per  cent,  iron  and  4.3  per  cent,  carbon.     In  the  study  of  the 
iron-carbon  alloys,  however,  we  have  to  take  into  account  the 
solid  solution  which  forms.     That  is  to  say,  we  must  remember 
that  iron  never  separates  from  the  liquid  state  without  carrying 
2.2  per  cent,  of  carbon  with  it  in  solid  solution.1     It  will  be  remem- 
bered that  when  lead  separated  from  the  liquid  solution,  it  carried 
with  it  a  small  amount  of  tin  as  an  impurity;  and  that  when  tin 
separated,  it  carried  with  it  a  small  amount  of  lead  as  an  impurity; 
but  we  disregard  these  traces  of  impurity  for  the  sake  of  simplicity 
in  outlining  the  laws  of  solutions.     In  the  case  of  iron-carbon 
alloys,  however,  the  2.2  per  cent,  of  carbon  carried  out  with  the 
iron  in  solid  solution,  substantially  as  an  impurity,  is  too  impor- 
tant in  its  effect  upon  the  material  to  permit  us  to  neglect  it. 

2.  The  line  X  Y  therefore  divides  the  diagram  in  Fig.  238  into 
two  parts.     Everything  to  the  left  of  this  line  freezes  as  a  solid 
solution  and  the  laws  are  similar  to  the  freezing  laws  of  the  gold- 
silver  alloys.     Everything  to  the  right  of  the  line  X  Y  freezes 
selectively,  according  to  the  same  laws  as  those  given  in  the  case 
of  the  lead-tin  alloys.     It  is  because  of  this  difference  in  the  freez- 
ing of  the  alloys  that  the  line  X  Y  is  arbitrarily  considered  as  the 


solid  solution  may  consist  of  carbon  dissolved  in  the  iron,  or  of 
iron  carbide  dissolved  in  the  iron.  We  do  not  know  definitely  which,  but  it 
is  not  necessary  to  discuss  this  question  just  yet. 


THE   SOLUTION  THEORY  OF   IRON  AND  STEEL         305 

dividing  line  between  steel  and  cast  iron.  That  is  to  say,  all  the 
alloys  with  less  than  2.2  per  cent,  carbon  are  defined  as  steel,  and 
alj  with  more  than  2.2  per  cent,  carbon  are  defined  as  cast  iron. 

3.  Freezing  of  Steel.  —  All  the  steels  freeze  as  solid  solutions. 
//  Let  us  consider  a  solution  of  99.5  per  cent,  iron  and  0.5  per  cent. 

carbon  at  1650°  C.  This  will  be  represented  by  the  point  b  in  Fig. 
238.  This  cools  until  it  meets  the  line  A  B,  and  now  it  commences 
to  solidify.  For  a  few  degrees  of  temperature  it  is  part  liquid  and 
part  solid,  but  by  the  time  it  has  fallen  to  a  temperature  where  it 
meets  the  line  A  a,  it  has  become  entirely  solid,  and  it  is  now  a 
homogeneous  solution  of  0.5  per  cent,  of  carbon  in  iron.  Consider 
next  a  solution  containing  99  per  cent,  of  iron  and  1  per  cent,  of 
carbon,  at  the  point  c  in  Fig.  238.  When  this  cools  to  the  tempera- 
ture where  it  crosses  the  line  A  B  it  commences  to  solidify,  and  it 
is  in  a  partly  liquid  and  partly  solid  condition  until  it  drops  to  a 
temperature  where  it  crosses  the  line  A  a,  upon  which  solidification 
is  complete,  and  it  now  becomes  a  homogeneous  solution  of  1  per 
cent,  carbon  in  iron.  The  same  actions  take  place  with  an  alloy 
containing  98.5  per  cent,  iron  and  1.5  per  cent,  carbon  (the  point  d 
in  Fig.  238),  and  also  in  the  case  of  98  per  cent,  iron  and  2  per  cent, 
carbon.  In  all  these  alloys  we  finally  arrive  at  a  solid  solution  of 
carbon  in  iron.1  To  this  solid  solution  the  name  of  'austenite' 
is  given,  and  this  name  applies  no  matter  how  much  or  how  little 
carbon  is  in  solid  solution.  In  other  words,  all  the  steels  are  in 
the  condition  of  austenite  as  soon  as  their  solidification  is  complete. 

4.  Freezing  of  Cast  Iron.  —  The  freezing  of  cast  iron  is  shown 
by  the  diagram  to  the  right  of  the  line  X  Y,  and  if  we  should  con- 
sider this  part  as  a  separate  diagram,  then  it  would  be  similar  to 
Fig.  235,  the  freezing  of  the  lead-tin  alloys.     There  is  one  differ- 
ence to  be  borne  in  mind,  however:  along  the  line  A  B  in  Fig.  235 
we  had  a  selective  precipitation  of  lead;  along  the  line  A  B  in  Fig. 
238  we  have  a  selective  precipitation,  not  of  pure  iron,  but  of  iron 
containing  2.2  per  cent,  of  carbon.     In  other  words,  this  entity, 
consisting  of  a  solid  solution  of  iron  with  2.2  per  cent,  of  carbon, 
behaves  as  if  it  were  an  elemental  substance.     Suppose  we  have, 

1  The  formation  of  the  solid  solutioh  from  the  liquid  solution  is  discussed 
in  detail  in  Professor  Howe's  'Iron,  Steel  and  Other  Alloys/  but  it  requires 
too  much  space  to  be  discussed  here.  For  our  purpose  it  is  sufficient  to  know 
that  when  freezing  is  completed,  we  have  a  homogeneous  solid  solution  of  all 
of  the  carbon  in  all  of  the  iron. 


306  THE  METALLURGY  OF   IRON  AND  STEEL 

for  example,  a  liquid  solution  of  2.5  per  cent,  of  carbon  in  iron  at 
a  temperature  of  1400°  C.  This  will  be  represented  by  the  point  e 
in  Fig.  238.  The  liquid  solution  will  cool  until  it  reaches  a  tem- 
perature of  about  1320°  C.  At  this  point  there  will  begin  to  pre- 
cipitate the  entity  of  which  I  have  spoken,  namely,  iron  contain- 
ing 2.2  per  cent,  carbon  in  solution.  This  precipitation  will  cause 
the  liquid  solution  to  be  impoverished  in  iron,  and  it  will  therefore 
move  to  the  right  in  the  diagram  as  the  temperature  falls ;  or,  in 
other  words,  it  will  travel  down  the  line  A  B.  By  the  time  the 
temperature  of  1135°  C.  is  reached,  a  large  amount  of  the  entity 
containing  2.2  per  cent,  of  carbon  will  have  precipitated,  and  the 
small  amount  of  liquid  solution  left  will  be  at  the  point  B,  that  is, 
the  eutectic  point,  where  there  is  4.3  per  cent,  carbon.  With 
further  cooling  the  eutectic  will  cross  the  point  B,  and  therefore 
will  complete  its  precipitation  and  its  freezing.  It  breaks  up  into 
crystals,  part  of  which  consist  of  tiny  flakelets  of  the  entity  before 
mentioned  —  iron  containing  2.2  per  cent,  carbon  —  and  the 
other  part  of  crystals  of  graphite  — i.e.,  carbon. 

5.  A  similar  result  will  be  obtained  in  the  case  of  a  3  per  cent, 
liquid  solution  of  carbon  in  iron.     This  will  cool  until  it  reaches 
1280°  C.,  where  the  same  entity  will  precipitate,  decreasing  the 
residual  solution  in  iron  so  that  it  travels  down  the  line  A  B  and 
finally  reaches  the  point  B,  after  which  this  eutectic  solution  at 
the  point  B  will  precipitate  as  before. 

6.  We  may  sum  up  paragraphs  4  and  5  by  saying  that  any 
solution  of  iron  containing  more  than  2.2  per  cent,  and  less  than 
4.3  per  cent,  of  carbon  will  consist,  after  freezing,  of  a  eutectic 
together  with  a  certain  amount  of  previously  precipitated  entity 
(consisting  of  iron  with  2.2  per  cent,  of  carbon  in  solid  solution). 

7.  What  will  occur  in  case  the  solution  contains  more  than  4.3 
per  cent,  of  carbon?1     Take,  for  example,  a  liquid  solution  con- 
taining 4.7  per  cent,  of  carbon  at  a  temperature  of  1200°  C.    This 
will  cool  until  a  temperature  of  about  1170°  is  reached  and  the  line 
C  B  is  met.   As  cooling  proceeds  to  lower  temperatures,  carbon  (i.e., 
graphite)  precipitates  out  and  the  liquid  solution  remaining  moves 
to  the  left  in  the  diagram.     That  is  to  say,  it  travels  down  the 
line  C  B.  When  the  temperature  1135°  is  reached,  so  much  graphite 
is  precipitated  that  the  residual  solution  is  now  of  the  eutectic  pro- 

1  It  is  very  seldom  that  solutions  contain  more  than  4.3  per  cent,  of  carbon, 
because  this  much  carbon  does  not  readily  dissolve  in  iron. 


THE   SOLUTION  THEORY  OF   IRON  AND   STEEL 


307 


portions.  With  further  cooling,  this  eutectic  breaks  up  as  before, 
consisting  thereafter  of  crystals  of  graphite  and  of  the  entity  com- 
posed of  iron  with  2.2  per  cent,  of  carbon  in  solid  solution. 

8.  Summary.  —  To  sum  up,  then,  all  the  solutions  of  iron  and 
carbon  containing  less  than  2.2  per  cent,  of  carbon  will  consist, 


1600°C 
A 

1400° 
1300° 
1000° 
800° 

600° 

i 
1C 

2912°F 
2552° 
2192° 
1832° 
1472° 
1112° 

b 

c 

>! 

-< 

V 

SS»» 

d 
"fcfcfc 

z 

1 

X 

^ 

> 

^ 

v^ 

^ 

\ 

^v 

^ 

V^ 

C 

\ 

\ 

^ 

^B^ 

^ 

Ellt€ 

ctic  fre 

ezes 

D 

)*                      1%  Carbon        2% 
K)  %  Iron          99£lron 

3%                   4*                5*Carbon 
95*Iron 

FIG.  238.  — THE  FREEZING  OF  ALLOYS  OF  IRON  AND  CARBON. 

after  solidification,  of  a  solid  solution  of  iron  and  carbon  having 
the  same  chemical  composition  as  the  original  liquid  solution,  and 
being  a  homogeneous  solution  of  one  in  the  other.  There  can  be 
no  eutectic  formed  if  there  is  not  more  than  2.2  per  cent,  carbon. 
All  the  solutions  with  more  than  2.2  per  cent,  of  carbon  will  con- 
sist, after  solidification,  of  a  eutectic  together  with  a  certain 
amount  of  previously  precipitated  graphite  or  of  the  previously 


308  THE  METALLURGY  OF   IRON  AND  STEEL 

precipitated  entity  mentioned  (iron  with  2.2  per  cent,  of  carbon  in 
solid  solution). 

9.  Effect  of  Silicon  and  Sulphur.  —  Silicon  and  sulphur  have 
an  important  effect  upon  the  changes  that  occur  in  the  solidifica- 
tion of  the  iron-carbon  alloys.     Silicon  has  the  effect  of  pushing 
the  point  B,  Fig.  238,  to  the  left.     In  other  words,  it  causes  the 
eutectic  to  have  less  carbon  than  4.3  per  cent.     It  thus  lessens 
the  amount  of  total  carbon  that  cast  iron  usually  contains.     Silicon 
seems  to  have  the  effect  of  pushing  the  point  a  also  to  the  left  and 
thus  decreasing  the  amount  of  carbon  that  solidifies  in  the  solid 
solution.     In  fact,  we  may  have  iron  containing  2  or  3  per  cent,  of 
silicon  in  which  the  iron  will  solidify  with  only  a  small  amount  of 
carbon  dissolved  in  it.     Sulphur  has  the  opposite  effect  and  tends 
to  push  the  point  B  to  the  right  and  to  increase  the  total  carbon. 

10.  Rate  of  Cooling.  —  The  changes  represented  in  Fig.  238 
take  place  very  slowly.     This  is  of  great  importance,  because  it 
renders  it  necessary,  in  order  that  these  changes  may  occur,  that 
the  cooling  of  the  solutions  shall  be  very  slow.     In  other  words, 
if  we  cool  rapidly  we  will  not  get  a  precipitation  of  graphite,  even 
when  the  eutectic  freezes,  but  will  obtain  a  solid  solution  contain- 
ing all  the  carbon.     This  solid  solution,  of  course,  is  not  in  a  normal 
condition,  and  theoretically  should  never  be  formed  to  this  ex- 
tent, but  is  none  the  less  present  in  many  cases,  because  the  cooling 
was  not  slow  enough.     As  already  noted,  however,  the  presence 
of  silicon  hastens  the  precipitation  of  graphite,  so  that  silicon  in 
this  sense  takes  the  place  of  slow  cooling,  and  in  our  high-silicon 
pig  irons  we  often  have  a  precipitation  of  almost  all  the  carbon 
as  graphite.     In  other  words,  we  have  only  a  very  small  amount 
of  solid  solution  formed,  which  probably  does  not  contain  as  much 
as  2.2  per  cent,  carbon. 

THE  SOLID  SOLUTION  OF  IRON  AND  CARBON 

We  have  seen  that  every  alloy  of  iron  and  carbon  contains, 
after  solidification,  a  varying  amount  of  the  solid  solution  of  iron 
and  carbon.  For  example,  if  we  started  with  1  per  cent,  of  carbon, 
then,  immediately  after  solidification,  we  would  have  a  solid  solution 
of  1  per  cent,  carbon  in  iron ;  if  we  started  with  1 .5  per  cent,  of  carbon, 
we  would  have  a  solid  solution  containing  1.5  per  cent.;  if  we 
started  with  2.2  per  cent,  of  carbon,  then  we  would  have  a  solid 


THE  SOLUTION  THEORY  OF   IRON  AND   STEEL         309 

solution  of  2.2  per  cent,  carbon.  Even  if  we  start  with  more,  than 
2.2  per  cent,  carbon,  then  the  alloy,  after  solidification,  will  con- 
sist partly  of  a  solid  solution  containing  2.2  per  cent,  of  carbon 
and  partly  of  graphite. 

Now,  what  becomes  of  these  solid  solutions  which  make  up  a 
part  or  a  whole  of  the  cast  iron  and  steel  alloys  when  they  freeze? 
Does  the  carbon  remain  in  solid  solution  down  to  the  atmos- 
pheric temperature,  or  does  it  precipitate,  or  does  it  undergo 
some  other  change?  We  find  by  experiment  that  the  solid  solu- 
tions do  not  survive,  but  precipitate  at  a  lower  temperature,  and 
the  laws  governing  the  decomposition  of  these  solid  solutions  are 
similar  to  the  laws  governing  the  decomposition  of  liquid  solu- 
tions —  for  example,  of  the  lead-tin  solutions.  In  short,  we  have 
again  a  series  of  curves  showing  the  selective  precipitation  of  the 
constituents  of  these  solid  solutions,  and  the  only  difference  be- 
tween the  nature  of  these  curves  and  the  lead-tin  curves  is  that 
these  represent  changes  taking  place  in  the  solid  state,  while  the 
lead-tin  curves  represent  changes  taking  place  in  the  liquid  state. 

Nature  of  the  Solid  Solution.  —  In  the  footnote  on  page  304  I 
called  attention  to  the  fact  that  the  solid  solution  of  iron  and 
carbon  might  be  a  solution  of  pure  carbon  in  iron,  or  a  solution  of  a 
carbide  of  iron  in  iron,  for  example,  of  FeaC  in  iron.  Several 
authorities  hold  this  view,1  while  others  maintain  that  the  solution 
is  of  elemental  carbon  in  iron.  The  question  is  of  more  academic 
than  practical  interest.  The  important  thing  is  that,  when  the 
solution  decomposes,  it  is  a  carbide  of  iron  which  precipitates. 
Those  who  believe  that  the  solid  solution  is  composed  of  elemental 
carbon  and  iron  explain  the  precipitation  of  the  carbide  by  main- 
taining that  when  the  carbon  separates  from  solution,  it  immedi- 
ately unites  with  iron  and  forms  a  carbide,  usually  FesC.  With 
this  explanation  I  shall  hereafter,  for  simplicity's  sake,  discuss  the 
solid  solutions  as  if  they  were  FeaC  in  iron. 2 

1  Indeed  one  authority  believes  that  there  are  probably  several  different 
carbides  (Fe3C,  FeaC,  FeC)  dissolved  in  the  iron. 

2  It  may  be  that  when  the  solid  solution  is  very  hot,  it  consists  of  elemental 
carbon  dissolved  in  iron,  but  that  as  it  falls  to  near  the  point  where  it  begins 
to  decompose,  it  consists  of  iron  carbide  dissolved  in  iron.     This  is  the  case 
with  the  solutions  of  table  salt  in  water  which,  at  a  high  temperature,  con- 
sists of  sodium  and  chlorine  dissolved  in  water;  near  the  freezing-point,  how- 
ever, the  sodium  and  chlorine  combine  and  the  solutions  consist  of  sodium 
chloride  dissolved  hi  water. 


310 


THE  METALLURGY  OF   IRON  AND  STEEL 


The  Decomposition  of  the  Solid  Solutions.  —  The  curves  of  de- 
composition of  the  solid  solutions  are  shown  in  Fig.  239.  The  line 
G  0  S  is  the  line  upon  which  there  is  selective  precipitation  of  pure 
To  this  pure  iron  the  name  of  '  ferrite  '  has  been  given  by 


iron. 


Professor  Howe,  and  this  name  meets  with  universal  acceptance. 


1600°C 
1400° 
1200° 

1000° 
G 

800° 

M 

600° 

C 
10 

: 

: 

2912F 
2552° 
2192° 
1832° 

1472° 
K 
1112° 

a 
/ 

\JL 

/E 

\t 

7 

5 

o 

Ns 

/ 

p 

1*  Carbon       2% 
0£Irou          99  4  Iron 

3%                     M                 5*  Carbon 
95  £  Iron 

FIG.  239.  —  DECOMPOSITION  CURVES  OF  THE  SOLID  SOLUTIONS  OF 
IRON  AND  CARBON.    (ALSO  KNOWN  AS  THE  CRITICAL  POINTS.) 

Consider  first  a  solid  solution  containing  0.40  per  cent,  of  carbon 
at  a  temperature  of  800°  C.  This  will  be  at  the  point  h  in  Fig.  239. 
It  will  cool  until  it  reaches  a  temperature  of  about  780°  C.  upon 
which  ferrite  will  begin  to  precipitate.  As  the  temperature  con- 
tinues to  fall  more  and  more  ferrite  precipitates,  which  impover- 
ishes the  solid  solution  in  iron  and  causes  it  to  travel  down  the 


THE   SOLUTION  THEORY   OF   IRON   AND   STEEL          311 

line  0  S.  By  the  time  the  temperature  has  reached  690°,  the  solid 
solution  has  reached  the  point  S,  corresponding  to  0.90  per  cent, 
carbon. 

Consider  next  an  alloy  containing  1.60  per  cent,  carbon  at 
1000°  C. :  this  will  be  at  the  point  k.  It  will  cool  until  it  reaches  a 
temperature  of  about  970°,  at  which  carbide  of  iron  (FeaC)  will 
begin  to  precipitate.  This  precipitation  continues  as  the  tem- 
perature falls,  constantly  decreasing  the  amount  of  carbon  in 
the  solid  solution,  which  therefore  travels  down  the  line  ES 
until,  at  690°,  it  reaches  the  point  S,  where  there  is  0.90  per  cent, 
carbon. 

A  similar  precipitation  will  take  place  with  all  of  the  solid 
solutions  of  iron  and  carbon:  if  they  contain  less  than  0.90  per 
cent,  carbon,  they  will  begin  to  precipitate  out  ferrite  when  they 
fall  to  the  line  GO  S.  If  they  contain  more  than  0.90  per  cent,  car- 
bon, they  will  begin  to  precipitate  carbide  of  iron  when  they  meet 
the  line  E  S.  In  either  case  the  residual  solid  solution  will  travel 
down  the  line  G  0  S,  or  else  E  S,  until  it  reaches  the  point  S  when 
the  temperature  has  fallen  to  690°  C. ;  we  will  then  have  some  solid 
solution  left  containing  0.90  per  cent,  carbon,  and  mixed  with 
this  some  previously  precipitated  ferrite  or  cementite,  as  the  case 
may  be. 

Eutectoid.  —  The  alloy  containing  0.90  per  cent,  carbon  is 
known  as  the  'eutectoid  alloy/  a  name  invented  by  Professor 
Howe  to  indicate  that  the  formation  of  this  alloy,  which  results  by 
selective  precipitation  of  the  solid  solution,  is  similar  to  the  forma- 
tion of  the  well-known  eutectics  of  liquid  solutions.  When  this 
eutectoid  solid  solution  cools  below  690°  C.,  it  is  completely  de- 
composed into  its  constituents,  ferrite  and  cementite.  These 
constituents  precipitate  in  tiny  flakelets,  which  arrange  themselves 
in  the  banded  structure  already  familiar  to  us  as  the  structure  of 
eutectics.  A  magnified  view  of  the  structure  is  shown  in  Fig.  241, 
while  Fig.  242  shows  the  magnified  structure  of  a  piece  of 'steel  com- 
posed of  a  eutectoid  together  with  previously  precipitated  ferrite ; 
and  Fig.  243  shows  the  structure  of  a  steel  consisting  of  the  eutec- 
toid with  previously  precipitated  cementite. 

It  will  be  evident  that  there  will  be  some  of  the  eutectoid  in 
every  piece  of  iron  or  steel,  for  even  the  cast  irons  contain,  after 
solidification,  a  certain  amount  of  solid  solution  which  precipi- 
tated either  while  the  liquid  alloy  was  traveling  down  the  line  A  B, 


312  THE  METALLURGY  OF   IRON  AND   STEEL 

or  during  the  freezing  of  the  liquid  eutectic  (containing  4.3  per  cent, 
of  carbon),  or  both.  The  formation  and  characteristic  of  this 
eutectoid  are  therefore  of  very  great  importance.  Its  presence  in 
iron  and  steel  was  known  long  before  the  theories  that  I  have  out- 
lined in  this  chapter  had  begun  to  be  understood,  and  the  name 
of  'pearlite'  was  given  to  it  because,  under  certain  circumstances, 
it  has  the  appearance  of  mother-of-pearl.  The  name  pearlite  is 
only  used  to  designate  the  eutectoid  after  its  complete  decomposi- 
tion and  the  separation  of  the  ferrite  and  cementite  into  the  banded 
structure  shown  in  Fig.  241. 


THE  COMPLETE  ROBERTS-AUSTEN,  ROOZEBOOM  DIAGRAM 

We  may  now  take  the  diagrams  of  Figs.  238  and  239  and  com- 
bine them  into  one  diagram  which  shall  represent  all  the  known 
changes  in  the  heating  and  cooling  of  iron  and  steel.1 

All  the  lines  drawn  in  Figs.  238  and  239  show  the  temperatures 
of  the  changes  during  cooling. 

Explanation  of  Fig.  246.  —  In  Fig.  246  we  have  an  assembly  of 
the  curves  showing  the  changes  in  the  liquid  and  in  the  solid  state. 
It  is  to  be  observed  that  the  dotted  line  E  F  is  somewhat  doubtful. 
It  was  drawn  in  by  Prof.  H.  W.  Bakhuis-Roozeboom  in  the 
belief  that  the  solid  solution  of  iron  containing  2.2  per  cent,  of 
carbon  began  to  decompose  at  1000°  C.  during  cooling.  There  is 
no  direct  evidence  in  favor  of  this  opinion,  however,  although 
certain  theoretical  considerations  are  in  favor  of  it ;  but  we  are  not 
warranted  in  assuming  them  as  proven.  Indeed,  the  changes  that 
take  place  in  the  alloys  and  at  the  temperatures  between  a  C  and 
S  K  are  yet  very  much  in  doubt,  and  several  different  theories  are 
held.  If  we  leave  out  the  line  E  F,  then  the  line  S  E  would  be 

1  For  it  is  to  be  understood  that  the  changes  that  I  have  spoken  of  as 
taking  place  during  the  cooling  are  exactly  reversed  during  heating.  It  is  to 
be  observed,  however,  that  the  changes  that  take  place  during  heating  occur 
at  a  somewhat  higher  temperature  than  the  reverse  changes  during  cooling. 
This  difference  is  probably  due  to  a  slight  lag,  so  that  the  changes  occur  a 
little  below  the  normal  temperature  during  cooling  and  a  little  above  the 
normal  temperature  during  heating.  This  lag  is  especially  noticeable  in  the 
changes  that  take  place  in  the  solid  solution,  and  there  is  a  difference  of  20°  or 
more  Centigrade  between  the  lines  GOS,  PS  K,  etc.,  if  they  are  observed 
during  heating. 


FIG.    240.  —  EUTECTIC    OF    COPPER 

AND   SILVER. 
(William  Campbell.) 


FIG.     241.  —  PEARLITE     EUTECTOID 
OF    IRON   AND    CARBON. 

(F.  Osmond.) 


FIG.  242.  —  PEARLITE  AND  FERRITE. 
250  diameters. 


FIG.  243.  —  PEARLITE  AND  CEMEN- 

TITE. 
250  diameters. 


FIG.    244.  —  PEARLITE.  FIG.    245.  —  PEARLITE. 

250  diameters.  1000  diameters. 

Picric  Acid. — Large  crystallization  due  to  long  overheating.     Polished  in  Relief. 


314 


THE  METALLURGY  OF  IRON  AND  STEEL 


extended  to  a,  as  I  have  shown  in  the  diagram,  and  the  solid 
solution  containing  2.2  per  cent,  of  carbon  will  commence  to  pre- 
cipitate its  cementite  immediately  after  solidification  is  completed 
(1135°  C.),  instead  of  135°  lower. 

Other  Lines  in  Fig.  246.  —  Certain  retardations  in  the  cooling 
curves  would  indicate  that  there  was  a  line  extending  all  the  way 


2912F 
2552° 

2192° 
D 

1832° 

1472° 
K 
1112° 

10UUC 
A 

1400° 

• 

1200° 

iooo 

G 

800° 
M 

600° 

( 
1( 

X 

^ 

^ 

\ 

\ 

^ 

^\ 

\ 

\ 

,**-*•" 

\ 

C 

X 

\ 

^ 

^^ 

^ 

/ 

/ 

/E 

F 

\ 

/ 

% 

/ 

)                      1*  Carbon        2*                     3%                   M                  5sS  Carbon 
NtitlOtt          99  #  Iron                                                                                    95^  Iron 

FIG.  246.— THE  FREEZING  AND  SOLID  DECOMPOSITION  CURVES 
OF  THE  IRON-CARBON  ALLOYS. 

across  this  diagram  at  about  775°  C.,  and  another  at  600°  C.  The 
significance  of  these  lines  is  as  yet  a  matter  of  speculation  merely, 
and  I  believe  it  to  be  well  to  disregard  them  in  this  brief  treatise 
until  we  are  able  to  offer  some  explanation. 

Roberts-Austen.  —  The  diagram  of  Fig.  246  is  often  known  as  the 
Roberts- Austen  diagram,  after  Sir  William  Roberts- Austen,  be- 


THE   SOLUTION  THEORY   OF   IRON  AND   STEEL         315 

cause  the  cooling  curves  that  located  the  lines  were  first  determined 
in  his  laboratory.1 

1  See  "  Proceedings  of  the  Institution  of  Mechanical  Engineers  "  (England), 
1897,  Fourth  Report  of  the  Alloys  Research  Committee,  Plate  2.  See  also 
'  Le  Fe  et  1'Acier  au  Point  de  Vue  de  la  Doctrine  des  Phases,"  H.  W.  Bakhuis- 
Roozeboom,  in  Zeitschrift  filr  physikalische  Chemie,vo\.  xxxiv,  p.  437:  French 
translation,  "  Contribution  a  TEtude  des  Alliages,"  pp.  327-386,  Paris,  1901. 


REFERENCES 
For  further  data  on  this  subject  see  especially  Nos.  1,  8,  9;  10. 


n  ^t 


XI 
THE   CONSTITUTION   OF   STEEL 

THE  properties  of  steel  depend  upon  the  chemical  composition 
of  its  constituents  as  well  as  upon  their  size  and  relation  to  one 
another.  Enough  has  been  said  to  show  that  steel  is  not  a  simple 
homogeneous  union  of  iron  with  varying  proportions  of  carbon, 
silicon,  manganese,  etc.;  but  is  built  up  of  individual  crystals 
somewhat  in  the  same  way  as  crystalline  rocks  are  formed  — 
granite,  for  example.  But  while  the  crystals  of  granite  are  gen- 
erally visible  to  the  naked  eye,  and  its  structure  may  therefore 
be  determined  by  a  more  or  less  cursory  examination,  the  structure 
of  steel  is  visible  only  by  means  of  the  microscope  and  after 
careful  polishing,  sometimes  followed  by  chemical  treatment  to 
differentiate  between  the  various  grains.  Nevertheless,  the  struc- 
ture of  steel  is  of  great  importance,  and  in  some  cases,  perhaps,  is 
even  more  so  than  the  chemical  composition. 

THE  MICRO-CONSTITUENTS  OF  STEEL 

In  this  chapter  I  shall  speak  only  of  slowly  cooled  steel  except 
where  I  have  indicated  the  contrary.  We  have  already  learned 
that  slowly  cooled  steel  must  necessarily  contain  ferrite  and 
cementite,  resulting  from  the  decomposition  of  the  solid  solution 
of  iron  and  carbon.  There  are  also  other  constituents  which  are 
found  under  the  microscope,  or  separated  by  chemical  analysis, 
or  in  both  ways.  These  latter  constituents  are  compounds  of  iron 
with  various  other  impurities,  such  as  iron  sulphide,  iron  phosphide 
and  iron  silicide;  or  of  two  impurities  with  each  other,  such  as 
manganese  sulphide. 

Ferrite.  —  Ferrite  is  theoretically  pure  iron,  and  especially 
iron  free  from  carbon.  It  is  weak  as  compared  with  several  of  the 
other  constituents,  having  a  tensile  strength  of  about  45,000  to 
50,000  Ibs.  per  square  inch;  it  is  also  very  soft  and  ductile,  re- 

316  * 


THE   CONSTITUTION   OF   STEEL  317 

sembling  copper  in  these  properties,  and  has,  furthermore,  a  high 
degree  of  malleability.  It  has  a  very  high  electrical  conductivity 
as  compared  with  the  other  constituents  of  iron  and  steel,  and 
about  one-seventh  the  conductivity  of  copper  and  silver,  the  best 
conductors  known.  (Copper  and  silver  are  of  nearly  the  same  con- 
ductivity.) Its  magnetic  force  is  the  highest  of  any  known 
substance,  its  magnetic  permeability  being  high,  and  its  hysteresis 
low.  It  crystallizes  in  the  isometric  system. 
.  Ferrite  is  an  important  constituent  of  all  steels  and  the  pre- 
dominant one  in  all  the  low-carbon  steels.  The  industrial  product 
approaching  nearest  to  pure  ferrite  is  wrought  iron,  if  we  disregard 
the  slag,  which,  being  mechanically  mixed  with  the  mass,  does 
not  appreciably  alter  its  chemical  and  physical  behavior.  It  is 
for  this  reason  that  wrought  iron  is  so  useful  where  a  soft  and 
ductile  material  is  necessary,  as  in  boilers,  for  instance;  or  where 
high  electrical  conductivity  is  demanded,  as  in  telegraph  wire; 
or  a  high  degree  of  magnetism,  as  in  the  cores  of  electromagnets. 
The  wrought  iron  made  in  Sweden,  and  known  as  'Norway 
iron/  is  greatly  preferred  for  this  latter  purpose,  on  account 
of  its  purity. 

Under  the  microscope  ferrite  may  be  distinguished  from 
cementite  by  its  softness.  If  steel  containing  these  two  con- 
stituents be  polished  on  damp,  rough  parchment,  or  on  chamois 
skin  stretched  over  a  soft  background  (as  wood),  the  ferrite  will 
wear  away  below  the  carbide  and  appear  in  intaglio.  The  same 
effect  will  be  obtained  by  Osmond's  ' polish  attack.'1  Ferrite 
is  also  distinguished  from  carbide  of  iron  by  the  fact  that,  after 
being  subjected  to  the  brief  action  of  certain  reagents,  such  as 
2  per  cent,  nitric  acid,  or  ordinary  commercial  tincture  of  iodine, 
the  ferrite  is  seen  in  darker  grains  and  the  carbide  in  bright  thin 
plates,  unattacked  by  the  reagent.  When  the  two  are  intimately 
associated  in  minute  grains,  as  in  pearlite,  the  carbide  appears 
bright  and  the  ferrite  dark,  because  eaten  away  below  the  surface 
by  the  reagent. 

Allotropic  Modifications.  —  There  is  one  peculiarity  of  pure 
iron,  or  ferrite,  which,  on  account  of  its  importance,  deserves 
special  attention,  namely,  its  ability  to  assume  different  allotropic 
modifications  at  different  temperatures.  The  nature  of  allo- 
tropism  has  already  been  explained  (see  page  486).  To  the  allo- 

1  See  page  453. 


318  THE  METALLURGY  OF   IRON  AND   STEEL 

tropic  modification  of  iron  the  names  of  'alpha/  'beta/  and 
'  gamma '  have  been  assigned.  The  alpha  modification  is  the 
one  existing  at  atmospheric  temperatures,  and  it  is  familiar  to 
all  who  make  or  use  iron.  If  this  be  heated,  however,  it  under- 
goes a  sudden  change  at  about  760°  C.  (1390°  F.).  This  change 
is  evidenced  by  an  absorption  of  heat  and  the  circumstance 
that  the  iron  loses  almost  entirely  its  power  to  attract  a  magnet; 
that  is  to  say,  it  becomes  about  as  non-magnetic  as  lead,  copper, 
etc.  The  change  in  magnetism  is  accompanied  by  a  change  in 
electrical  conductivity,  in  specific  heat  and  in  other  properties. 
In  short,  the  iron  has  changed  in  many  of  its  properties  without 
undergoing  any  alteration  in  chemical  composition.  This  new 
allotropic  modification  of  iron  is  known  as  beta  iron. 

If,  now,  beta  iron  be  further  heated  to  a  temperature  of  about 
890°  C.  (1634°  F.),  it  again  changes  several  of  its  properties  and 
becomes  what  is  known  as  gamma  iron.  Gamma  iron  differs 
from  beta  iron,  especially  in  electrical  conductivity  and  in  crystal- 
line form.  Ferrite  crystallizes  always  in  the  cubic  system,  and 
Osmond  1  and  Stead  2  have  studied  the  variations  of  form  assumed 
by  it  and  by  its  alloys  with  carbon.  Osmond  especially  has 
studied  the  crystallography  of  the  gamma,  beta,  and  alpha 
modifications  of  the  pure  metal.  Gamma  iron  does  not  crystallize 
isomorphously  with  either  beta  or  alpha  iron,  which  crystallize 
identically  in  cubes;  but  it  assumes  all  the  combinations  of  the 
cube  and  octahedron,  and,  in  the  latter  form  would  be  isomorphous 
with  carbon  in  the  diamond  form.  Therefore,  in  the  isomorphous 
mixtures  (i.e.,  solid  solutions)  of  iron  and  carbon  one  would 
expect  to  find  some  carbon  in  the  diamond  form,  which  has  indeed 
been  accomplished  by  Osmond.  This  is  used  as  an  argument  in 
favor  of  the  belief  that  the  solid  solution  is  with  carbon,  not 
with  cementite ;  for  Osmond  has  shown  3  that  cementite  does  not 
assume  any  crystalline  form  which  would  be  isomorphous  with 
ferrite.  Beta  and  alpha  iron  do  not  crystallize  isomorphously 
with  either  carbon  or  cementite,  which  accords  with  the  observed 
tendency  of  ferrite  to  begin  to  separate  from  the  solid  solution 
at  the  same  temperature  at  which  it  changes  from  gamma  to  beta 
iron. 

If  ferrite  is  in  the  gamma  form,  say  at  1000°  C.  (1832° 
F.),  then  it  will  undergo  upon  cooling  the  changes  which,  as  I 

1  See  No.  110,  page  332.  2  See  No.  181,  page  457.  »  See  No.  181. 


THE  CONSTITUTION   OF   STEEL 


319 


have  outlined,  it  undergoes  on  heating,  but  reversed.     That  is  to 

say,  at  about   890°  C.  (1634°  F.)  it  will   change   from   gamma 

to  beta  iron;  at   760°  (1390°  F.)  it  will  change  from  beta   to 

alpha  iron,  in  each  case  receiving  again  the  properties  which  it 

had  before  heating.     In  other  words,  the  change  'from  one  allo- 

tropic  form  to  another  is  a  reversible  change, 

taking  place  in  one  direction  on  cooling  and 

in  the  opposite  direction  on  heating.     The 

change  on  cooling  takes  place  at  a  slightly 

lower  temperature  than  on  heating.     This 

is  not  because  it  is  other  than  a  true  reverse 

action,   but  because   the   change    in   either 

direction  is  necessarily  slow  and  lags  a  little 

behind   the   temperature.     The    amount   of 

this  lag  will  vary  directly  with  the  speed  of 

heating  and  cooling. 

We  never  get  pure  gamma  iron  at  any 
temperature  unless  we  start  with  iron  free 
from  carbon,  because  gamma  ferrite  never 
separates  from  the  solid  solution.  If,  how- 
ever, we  have  a  solid  solution  of  iron  with, 
let  us  say,  0.2  per  cent,  of  carbon,  then  this 
solid  solution  will  begin  to  precipitate  fer- 
rite at  a  temperature  of  about  830°  C.  (1524° 
F.).  This  ferrite  will  be,  of  course,  in  the 
beta  form  and  will  be  non-magnetic  until 
the  mass  cools  below  760°  (1390°  F.),  when 
the  previously  precipitated  ferrite  will  change 
from  the  beta  to  the  alpha  form.  Any  fer- 
rite which  separates  from  solid  solution  after 
that  temperature  is  reached  will  separate  in 
the  first  instance  in  the  alpha  form.  For 
example,  if  we  have  a  solid  solution,  con- 
taining, say,  0.7  per  cent,  carbon,  this  will  commence  to  precipi- 
tate ferrite  below  760°  C.  (about  720°),  and  the  ferrite  will  be  in 
the  alpha  form.1 

1  Some  maintain  that  the  ferrite  always  precipitates  as  gamma  ferrite, 
then  immediately  changes  to  beta  and  next  to  alpha  ferrite.  Others 
maintain  that  when  the  solid  solution  is  cooled  near  the  line  G  O  S,  it  changes 
from  a  solid  solution  of  gamma  iron  into  a  solid  solution  of  beta  iron,  and  then 


FIG.  247.  — COOLING 
CURVE  OF  PURE 
IRON. 


320  THE  METALLURGY  OF   IRON  AND  STEEL 

Cementite.  —  The  carbide  of  iron,  Fe3C,  is,  next  to  ferrite, 
the  most  important  constituent  of  steel,  and  practically  all  of 
the  carbon  is  present  in  this  form.1  Cementite  is  very  hard  and 
brittle,  scratching  glass  with  ease  and  flying  into  pieces  under  a 
blow.  It  crystallizes  usually  in  thin  flat  plates,  which  are  large 
in  size  (sometimes  up  to  J  in.  in  diameter)  when  there  is  much 
cementite  present.  It  is  attacked  by  reagents  less  than  most 
of  the  other  constituents  and  is  in  this  way  distinguished  under 
the  microscope.  It  is  a  little  difficult  to  distinguish,  by  micro- 
scopic evidence  alone,  between  steel  consisting  of  pearlite  with  a 
slight  excess  of  cementite  and  steel,  consisting  of  pearlite  with  a 
slight  excess  of  ferrite.  The  practiced  eye  can  usually  tell;  but 
a  chemical  analysis  readily  distinguishes,  since  steel  with  less 
than  0.9  per  cent,  carbon  will  have  excess  ferrite  over  pearlite, 
and  that  with  more  than  0.9  per  cent,  will  have  excess  cementite. 

Cementite  contains  6.6  per  cent,  of  carbon,  or,  roughly,  is 
one-fifteenth  carbon.  We  may  therefore  tell  the  amount  of 
cementite  in  any  steel  by  multiplying  the  amount  of  carbon  by 
fifteen.2  Cementite  may  be  separated  from  steel  by  electrolysis.3 
It  is  magnetic  at  ordinary  temperatures,  but  not  above  700°  C. 
(1292°  F.). 

The  carbon  united  with  iron  in  cementite  has  been  given 
various  names,  such  as  '  cement  carbon/  or  '  carbon  of  cementa- 
tion' (because  of  its  prominent  appearance  in  cemented  steels), 
and 'carbon  of  the  normal  carbide/  ' annealing  carbon'  (because 
all  the  carbon  of  well-annealed  steels  will  usually  be  present  as 
cementite) . 

Manganiferous  Cementite.  —  Manganese  forms  a  carbide  having 
the  formula  Mn3C.  This  is  isomorphous  with  Fe3C,  and  we  often 
find  the  two  carbides  together  in  one  crystal.  The  name  cementite 
is  still  applied  to  this  crystal,  although  it  must  be  recognized  that 

into  a  solid  solution  of  alpha  iron,  from  which  alpha  iron  then  precipitates. 
These  questions  are  chiefly  academic  and  of  almost  no  practical  importance ; 
nor  is  it  yet  known  which  is  the  actual  order,  though  many  are  inclined  to 
agree  with  Professor  Sauveur  (see  No.  Ill)  upon  the  latter  order. 

1  There  is  not  wanting  evidence  in  favor  of  other  carbides  being  discovered, 
such  as  Fe2C  and  FeC. 

2  In  other  words,  steel  containing  0.5  per  cent,  of  carbon  will  contain  7.5 
per  cent,  cementite;  steel  containing  1  per  cent,  carbon  will  contain  15  per 
cent,  cementite;  etc. 

3  See  No.  112,  page  332. 


FIG.     248.  —  FERRITE,     PURE     IRON 

(ELECTROLYTIC.) 
1000  diameters.     Etched  with  picric  acid. 


FIG.  250.  —  BIG  CEMENTITE  CRYSTAL 

IN   PEARLITE. 

Magnified    250    diameters.     Polished    in 
relief. 


PIG.  252.  —  ELONGATED  BUBBLE  OF 

MANGANESE   SULPHIDE. 
Magnified    250    diameters.     Unetched. 


FIG.  249.  —  PEARLITE  CRYSTALS. 

Surrounded    by    ferrite.     Magnified    250 

diameters.     Etched  with  HNO3. 


FIG.  251.  —  CRYSTALS  OF  MANGA- 

NIFEROUS   CEMENTITE. 

Magnified    50    diameters.     Etched    with 

nitric  acid. 


FIG.  253.  — EUTECTIC  OF  Fe3P  AND 

IRON. 

Magnified  1000  diameters.     Etched  with 
picric  acid. 


322  THE  METALLURGY  OF   IRON   AND   STEEL 

a  part  of  the  iron  has  been  replaced  by  manganese,  and  the  formula 
for  the  compound  is  usually  written  (FeMn)3C.  The  amount 
of  manganese  in  these  crystals  is  very  variable,  running  almost 
all  the  way  from  nothing  to  100  per  cent.  As  manganese  has  an 
atomic  weight  almost  the  same  as  that  of  iron  (Mn  55,  Fe  56),  one 
weight  of  manganese  will  replace  almost  exactly  an  equal  weight 
of  iron  in  the  crystal.  The  peculiarity  of  the  manganiferous 
cementite  is  that  the  crystals  of  free  cementite  are  liable  to  be 
larger,  especially  when  the  proportion  of  manganese  is  large, 
and  are  seemingly  harder  and  more  difficult  to  machine. 

Manganese  Sulphide.  —  Manganese  and  sulphur  unite  to 
form  manganese  sulphide,  having  the  formula  MnS,  and  this 
compound  is  found  in  all  steels.  Indeed,  all  of  the  sulphur  will 
be  found  in  this  combination,  provided  there  is  enough  manganese 
in  the  steel  to  unite  with  it.  It  is  necessary  to  have  more  than 
the  theoretical  amount  of  manganese  for  this  purpose,  however, 
because  unless  there  is  a  surplus  present,  the  attraction  of  the 
manganese  for  the  sulphur  does  not  seem  to  be  always  sufficient 
to  catch  it  all.  Steel  should  therefore  always  contain  about  four 
times  as  much  manganese  as  sulphur,  because  it  is  advantageous 
to  have  the  sulphur  all  in  the  form  of  manganese  sulphide. 

Manganese  sulphide  is  seen  under  the  microscope  as  a  dove- 
gray  substance  before  the  polished  material  is  etched  with  any 
reagents.  It  is  usually  collected  together  in  round  drops,  which 
are  sometimes,  if  large  in  size,  seen  to  be  elongated  by  the  rolling 
or  hammering  of  the  material  (see  Fig.  152). 

Manganese  tends  to  make  the  crystals  of  steel  smaller,  which 
is  advantageous,  but  makes  the  metal  more  liable  to  crack  in 
heating,  and  still  more  so  in  cooling  suddenly  from  a  red  heat. 

Iron  Sulphide.  —  The  bulk  of  the  sulphur  not  united  with  the 
manganese  will  be  found  in  the  form  of  iron  sulphide,  FeS.  This 
iron  sulphide  is  more  brittle  than  manganese  sulphide,  and 
instead  of  coalescing  in  drops,  it  spreads  out  in  webs  or  sheets. 
It  is  therefore  very  weakening  to  the  steel,  because  the  area  of 
weakness  is  more  extensive  than  the  tiny  spots  of  manganese 
sulphide.  Steel  containing  iron  sulphide  is  liable  to  show  poor 
tensile  test  and  low  ductility.  It  is  at  the  rolling  temperature, 
however,  that  iron  sulphide  produces  the  greatest  weakness, 
because  at  this  point  it  is  in  a  liquid  form  and  therefore  has 
practically  no  adhesion  to  the  crystals  of  steel,  which  are  liable 


THE  CONSTITUTION   OF   STEEL  323 

to  break  along  the  planes  or  meshes  of  sulphide.  The  same  is 
true,  to  a  less  extent,  of  the  effect  of  manganese  sulphide,  which 
is  also  in  a  liquid  or  pasty  condition  at  the  rolling  temperature; 
but  the  extent  of  its  damage  is  not  so  great  on  account  of  its 
drawing  together  in  drops.1  These  facts  explain  the  well-known 
beneficial  effect  of  manganese  in  counteracting  the  damage  due  to 
sulphur  in  iron  and  steel. 

Iron  Phosphide.  —  Iron  forms  at  least  one  phosphide,  having 
the  formula  FesP,  and  this  phosphide  forms  with  iron  a  series  of 
alloys,  of  which  the  eutectic  contains  64  per  cent,  of  Fe3P  (10.2  per 
cent,  of  phosphorus).  This  results  in  a  considerable  lowering  ot 
the  melting-point  of  iron  for  each  addition  of  phosphorus.  Even 
1  per  cent,  of  phosphorus  will  make  the  melting-point  of  the 
metal  very  much  lower,  and  it  is  for  this  reason  that  foundry  irons 
are  often  desired  with  a  high  content  of  phosphorus.  Even 
where  there  is  a  smaller  amount  of  phosphorus,  there  will  be  some 
of  the  phosphorus  eutectic  formed,  and  this  remains  in  a  molten 
condition  for  some  time  after  the  bulk  of  the  steel  has  solidified. 
This  liquid  eutectic  tends  to  migrate  to  the  spaces  between  the 
crystals,  where  it  remains  after  solidification  and  forms  a  very 
brittle  network,  which  naturally  makes  the  whole  mass  more  or 
less  brittle.  For  these  reasons  phosphorus  is  the  greatest  source 
of  brittleness  in  steel,  and  especially  brittleness  under  shock, 
and  is  thus  a  great  enemy  to  the  engineer  and  other  users  of 
the  material. 

Besides  forming  the  eutectic,  as  I  have  described,  phosphorus 
also  tends  to  produce  coarse  crystallizations  in  steel,  and  this 
makes  it  both  weak  and  brittle.  It  is  a  fact  observed  many 
times  that  the  embrittling  effect  of  phosphorus  on  steel  is  much 
less  when  the  steel  is  very  low  in  carbon,  and  as  the  carbon  rises 
so  the  brittleness  caused  by  phosphorus  rises.  This  and  other 
effects  of  phosphorus  have  been  explained  by  Prof.  J.  E.  Stead 
in  two  very  able  papers.2  He  has  shown  that  a  little  phosphorus 
will  dissolve  in  ferrite  and  that  then  the  eutectic  which  produces 
the  brittleness  will  not  form,  but  as  the  carbon  in  the  steel  in- 
creases, it  precipitates  the  phosphorus  from  the  ferrite  solid 
solution  and  therefore  causes  the  eutectic  to  form.  Hence,  the 
more  ferrite  and  the  less  cementite  in  steel,  the  less  will  be  the 
brittleness  produced  by  phosphorus. 
1  See  No.  113,  page  332.  2  See  No.  184  on  page  157  and  No.  115  on  page  332. 


324  THE  METALLURGY  OF   IRON  AND   STEEL 

Iron  Silicides.  —  There  seem  to  be  three  or  more  silicides  of 
iron,  but  the  one  having  the  formula  FeSi  seems  to  be  found 
most  commonly  in  steel.  It  appears  to  increase  very  slightly 
the  strength  of  steel,  and  also,  to  a  limited  extent,  its  hardness. 
The  chief  importance  of  silicon,  however,  as  already  pointed  out, 
is  in  promoting  soundness. 

Iron  Oxides.  —  Oxygen  occurs  in  steel  in  the  form  of  FeO 
and  Fe.203.  In  either  form  its  presence  is  very  harmful,  producing 
brittleness  in  both  hot  and  cold  steel,  besides  causing  the  liability 
to  blow-holes  already  discussed.  There  is  probably  no  constit- 
uent more  harmful  to  steel  than  oxygen,  and  unfortunately  the 
chemists  are  far  behind  in  respect  of  not  yet  having  found  a 
satisfactory  method  of  accurately  determining  small  traces  of 
this  gas.  The  effect  of  oxygen  is  somewhat  similar  to  that  of 
sulphur  and,  in  common  parlance,  makes  the  steel  'rotten/ 

Nitrogen  and  Hydrogen.  —  Both  nitrogen  and  hydrogen  occur 
in  steel,  and  one  of  the  theories  to  explain  the  superiority  of 
crucible  steel  is  based  upon  the  relative  freedom  of  this  material 
from  these  two  gases.  The  amount  of  nitrogen  and  hydrogen 
present  is  usually  very  small.  Hydrogen  dissolves  very  easily 
in  iron  at  a  high  temperature,  but  is  evolved  in  part  as  the  metal 
cools.  In  order  to  obtain  entire  freedom,  however,  it  is  necessary 
to  heat  and  cool  several  times  in  vacuo. 

THE  STRENGTH  OF  STEEL 

The  properties  of  steel  most  commonly  desired  are  strength 
and  ductility.  Unfortunately  there  is  more  or  less  incompatibility 
between  these  two.  That  is  to  say,  as  the  strength  of  steel 
increases,  the  ductility  usually  decreases;  and,  conversely,  as  the 
ductility  increases,  the  strength  usually  decreases.  There  are 
other  properties  of  steel  which  are  likewise  of  importance,  either 
because  they  are  desired,  or  the  reverse.  Among  these  we  shall 
especially  discuss  hardness,  brittleness,  electric  conductivity,  mag- 
netic permeability,  magnetic  hysteresis,  permanent  magnetism 
and  weldability. 

Pure  iron  has  a  tensile  strength  of  about  45,000  Ibs.  per  square 
inch  and  a  compressive  strength  of  about  80,000  Ibs.  per  square 
inch.  These  are  increased  by  means  of  several  of  the  ordinary 
impurities  found  in  steel,  but  the  most  important  strengthener  is 


THE  CONSTITUTION   OF   STEEL 


325 


carbon,  because  this  will  give  the  maximum  increase  in  strength 
with  the  least  decrease  in  ductility. 

Carbon.  —  Each  increase  in  carbon  (cementite)  gives  an  in- 
crease in  tensile  strength  until  we  reach  a  maximum  of  about 
0.9  to  1  per  cent,  of  carbon  (13.5  to  15  per  cent,  cementite).  With 
further  increase  in  cementite  there  is  a  decrease  in  tensile  strength. 
It  is  probable  that  the  reason  for  this  maximum  of  tensile  strength 
at  approximately  the  eutectoid  ratio  of  the  steel  is  due  largely 


170,000 


140,000 


110,000 


80,000 


50,000 


Percentage  of  Carbon 
0.10  0.20  0.30  0.400.50  O.CO  0.70  0.80  0.90 l'00  1.10  1.20  1.30  1.40  1.50  1.60  1.70  1.80  1.90 


2.00 


RELATION  BETWEEN  THE  PHYSICAL 

CHARACTERISTICS  OF  STEEL  AND  THE 

PROPORTIONS  OF  FERRITE  AND  Fe3C 


00* 


80* 


<Fe300  5 

J  Ferrite    100  95 


30  £Fe3C 
70*Fenlte 


FIG.  254.     From  Howe,  "Iron,  Steel  and  other  Alloys." 


to  the  small  crystallization  and  the  intimate  mixture  of  the 
crystalline  constituents  when  the  steel  is  at,  or  near,  the  eutectoid 
proportions.1  With  less  cementite  the  grains  of  pearlite  are  sur- 
rounded by  a  network  of  ferrite;  with  more  cementite  the  grains 
of  pearlite  are  surrounded  by  a  network  of  cementite,  and  both 
of  these  networks  have  a  weakening  effect  upon  the  material  by 
decreasing  the  adhesion  of  the  crystals.  The  relation  between 
carbon  and  tensile  strength  is  shown  graphically  in  Fig.  254.2 

1  The  still  greater  increase  in  strength  when  the  two  constituents  of  the 
pearlite  (ferrite  and  cementite)  are  even  more  intimately  associated  is  ex- 
plained on  page  392.  2  See  page  438  of  No.  1  on  page  8  herein. 


326  THE  METALLURGY  OF  IRON  AND   STEEL 

H.  H.  Campbell  and  W.  R.  Webster  have  studied  exhaustively 
the  effect  of  the  different  impurities  upon  the  tensile  strength  of 
steel.  The  latest  word  on  this  subject  has  been  said  by  Campbell 
who  gives  1  the  following  rule  for  the  effect  of  each  0.01  per  cent, 
of  carbon  on  acid  and  on  basic  open-hearth  steel.  Starting  with 
40,000  Ibs.  per  square  inch  for  pure  steel,  each  0.01  per  cent,  of 
carbon  will  increase  the  strength  by  1000  Ibs.  per  square  inch  in 
the  case  of  acid  open-hearth  steel,  and  by  770  Ibs.  per  square 
inch  in  the  case  of  basic  open-hearth  steel.  Because  the  color 
method  of  determining  the  amount  of  carbon  does  not  show  all 
the  carbon  present,  the  figures  given  above  must  be  replaced  by 
1140  Ibs.  and  820  Ibs.  for  each  0.01  per  cent,  of  carbon,  when  the 
color  test  is  used.  We  have  no  data  to  determine  the  strengthen- 
ing effect  of  carbon  in  Bessemer  and  crucible  steel,  but  it  is  prob- 
able that  a  little  lower  value  than  that  given  for  basic  open-hearth 
steel  would  be  used  for  Bessemer,  and  a  little  higher  value  than  that 
given  for  acid  open-hearth  steel  would  be  used  for  crucible  steel. 

Silicon.  —  The  effect  of  silicon  on  strength  is  probably  very 
small  in  the  case  of  rolled  steel.  In  the  case  of  castings,  however, 
an  important  increase  in  tensile  strength  may  be  obtained  by 
increasing  the  silicon  to  0.3  or  0.4  per  cent.  This  practice  results 
in  practically  no  decrease  in  ductility,  but  it  is  necessary  to  supply 
larger  risers  on  account  of  the  deep  piping  that  will  be  produced. 
It  is  probable  that  the  beneficial  effect  of  silicon  in  this  case  is  due 
very  largely  to  its  producing  soundness. 

Sulphur.  —  H.  H.  Campbell  says  that  the  effect  of  sulphur  on 
the  strength  of  acid  and  basic  open-hearth  steel  is  very  small. 
It  is  probable,  however,  that  this  statement  is  only  true  when 
the  sulphur  is  in  the  form  of  manganese  sulphide,  because  the 
effect  of  iron  sulphide  would  be  to  lower  the  strength  and  the 
ductility  of  the  material.  The  worst  effect  of  sulphur  is  un- 
doubtedly its  production  of  '  red-shortness '  and  the  liability  to 
cause  checking  during  rolling,  or,  in  the  case  of  a  casting,  during 
cooling. 

Phosphorus.  —  Campbell  states  that  each  0.01  per  cent,  of 
phosphorus  increases  the  strength  of  the  steel  by  1000  Ibs.  per 
square  inch.  It  should  be  observed,  however,  that  this  increase 
of  strength  is  measured  by  the  resistance  of  the  material  to 
stresses  slowly  applied  and  that  it  ceases  with  0.12  per  cent. 
1  Page  391  of  No.  2,  page  8.- 


THE  CONSTITUTION  OF  STEEL  327 

phosphorus  and  is  reversed.  In  the  case  of  vibratory  stresses  and 
sudden  shocks,  phosphorus  is  probably  the  most  harmful  of  the 
elements,  so  that  it  is  undesirable  to  increase  the  strength  of  steel 
by  means  of  this  element.  This  is  the  more  true  because  of  the 
brittleness  produced  by  phosphorus,  for  an  increase  of  strength 
obtained  through  this  medium  is  accompanied  by  a  much  greater 
decrease  in  ductility  than  when  the  same  increase  in  strength  is 
obtained  through  the  medium  of  carbon. 

Manganese.  —  The  beneficial  effect  of  manganese  on  tensile 
strength  begins,  according  to  the  same  authority,  only  when  the 
manganese  is  above  0.3  or  0.4  per  cent.  With  less  manganese 
than  this,  in  the  case  of  open-hearth  and  Bessemer  steels,  the 
presence  of  some  other  condition,  probably  iron  oxide,  masks  the 
effect  of  manganese.  It  will  be  remembered  that  when  the  man- 
ganese is  low,  open-hearth  and  Bessemer  steels  are  harmfully 
charged  with  oxygen.  Furthermore,  the  effect  of  manganese 
is  dependent  upon  the  amount  of  carbon  present.  In  acid  open- 
hearth  steel  each  0.01  per  cent,  of  manganese  (beginning  at  0.4 
per  cent.)  increases  the  strength  80  Ibs.  per  square  inch  when  the 
carbon  is  0.1  per  cent.,  but  each  increase  of  0.01  per  cent,  of  carbon 
increases  the  strengthening  effect  of  manganese  by  8  Ibs.  So 
that,  for  example,  if  we  have  an  acid  open-hearth  steel  containing 
0.4  per  cent,  of  carbon,  then  each  0.01  per  cent,  of  manganese 
will  increase  the  strength  by  320  Ibs.  per  square  inch.  In  the 
case  of  basic  steel  each  0.01  per  cent,  of  manganese  (beginning 
at  0.3  per  cent.)  increases  the  strength  130  Ibs.  per  square  inch 
when  the  carbon  is  0.1  per  cent.,  and  so  on  to  250  Ibs.  per  square 
inch  when  the  carbon  is  0.4  per  cent.,  for  each  additional  0.01  per 
cent,  of  carbon  increases  the  strengthening  effect  of  manganese 
on  basic  steel  by  4  Ibs.  (See  Table  XXVI.) 

Formula?.  —  Campbell  gives  the  following  formulae  for  the 
strength  of  acid  and  basic  open-hearth  steels: 

For  acid  steel:  40,000+  lOOOC+lOOOP  +  xMn+R  =  ultimate  strength. 
For  basic  steel:  41,500+  770C  +  1000P+yMn+R  =  ultimate  strength. 

In  these  formulae,  0^=0.01  per  cent,  carbon  (determined  by  com- 
bustion), P  =  0.01  per  cent,  phosphorus,  Mn  =  0.01  per  cent, 
manganese,  and  R  =  a  variable,  depending  upon  the  heat  treat- 
ment which  the  steel  has  received.  For  X  and  Y  see  Table  XXVI. 
Copper.  —  Copper,  up  to  at  least  1  per  cent.,  does  not  appear 


328 


THE   METALLURGY   OF   IRON   AND   STEEL 


TABLE  XXVL— EFFECT  OF  EACH  0.01  PER  CENT.  MANGANESE 
ON  OPEN-HEARTH  STEEL 


PERCENTAGE  OF  CARBON 

On  Acid  Steel 

On  Basic  Steel 
Y 

Lbs.  per  sq.  in. 

Lbs.  per  sq.  in. 

0  05              

HO2 

0  10           

801 

130 

0  15 

120 

150 

0  20                   

160 

170 

0  25                  

200 

190 

0  30            

240 

210 

0  35  

280 

230 

0.40  

320 

250 

0  45 

360 

0  50                 

400 

0  55         .      

440 

0.60  

480 

1  Beginning  only  with  0.4  per  cent,  of  manganese. 

2  Beginning  only  with  0.3  per  cent,  of  manganese. 

to  have  any  important  effect  upon  the  strength  or  ductility  of 
low-  and  medium-carbon  steels,  but  increases  the  brittleness  of 
steel  containing  1  per  cent,  carbon.  When  the  sulphur  is  more 
than  0.05  per  cent,  copper  appears  to  make  the  steel  roll  less  easily 
and  above  0.5  per  cent,  of  copper  appears  to  make  high-carbon 
steel  draw  less  easily  into  wire. 

Arsenic.  —  Some  steels  contain  arsenic,  which  does  not  appear 
to  have  any  effect  when  it  is  below  0.17  per  cent.,  but  any  larger 
quantity  raises  the  tensile  strength  and  decreases  the  ductility  to 
a  very  important  extent. 

Oxide  of  Iron.  —  All  Bessemer  and  open-hearth  steels  contain 
more  or  less  oxide  of  iron,  there  probably  being  more  in  basic  steel 
than  in  acid,  and  more  in  Bessemer  steel  than  in  basic  open- 
hearth  steel.  It  is  probable  that  this  oxide  of  iron  has  not  any 
very  marked  effect  upon  strength,  as  Campbell  quotes  some  steels 
containing  quantities  larger  than  usual  whose  strength  is  good. 
No  data  are  given  as  to  the  ductility,  however,  and  it  is  probable 
that  oxide  of  iron  has  a  deleterious  effect  upon  this  quality. 

HARDNESS  AND  BRITTLENESS  OF  STEEL 

As  a  general  thing  the  hardness  and  brittleness  of  steel  increase 
together.  The  chief  commercial  application  of  this  property  is 
in  such  articles  as  railroad  rails  and  car- wheels,  bevel-  and  spur- 


THE  CONSTITUTION   OF   STEEL  329 

gears,  axles  and  bearings,  the  wearing  parts  of  crushing  machinery, 
etc.1  To  produce  hardness  in  these  materials  carbon  is  the  chief 
agent  used,  because  it  gives  the  maximum  hardness  with  the  least 
brittleness.  It  is  for  this  reason  that  railroad  rails  are  now  made 
up  to  0.7  per  cent,  carbon,  and  although  this  material  is  somewhat 
brittle  and  breakages  occasionally  occur,  the  high  carbon  is  de- 
manded in  order  that  the  head  of  the  rail  may  be  durable.  It  is 
probable  that  even  higher  carbon  than  this  would  be  used  if  it 
were  not  for  the  brittleness  already  in  the  ordinary  railroad  rails, 
due  to  the  fact  that,  being  made  by  the  acid  Bessemer  process,  they 
contain  nearly  0.1  per  cent,  phosphorus.  Phosphorus  increases 
both  the  hardness  and  the  brittleness,  especially  under  shock. 
Manganese  likewise  increases  hardness,  and  especially  the  kind 
of  hardness  which  makes  it  more  difficult  and  more  expensive  to 
machine  the  metal.  With  more  than  about  1  per  cent,  of  man- 
ganese the  steel  becomes  somewhat  brittle.  When  the  content 
rises  above  2  per  cent,  the  steel  is  so  brittle  as  to  be  practically 
worthless.  In  this  connection  a  curious  phenomenon  is  observed, 
in  that  a  still  further  increase  in  manganese  produces  a  reversal 
of  its  influence,  and  when  we  have  more  than  7  per  cent,  the 
metal  is  not  only  extremely  hard  and  practically  impossible 
to  machine  commercially,  but  becomes,  after  heat  treatment, 
very  ductile  and  tough.  This  will  be  considered  more  fully  in 
Chapter  XV. 

Silicon.  —  Silicon  makes  the  steel  slightly  harder,  but  ap- 
parently without  increasing  its  brittleness,  unless  we  have  more 
than  0.5  or  0.6  per  cent. 

ELECTRIC  CONDUCTIVITY  OF  STEEL 

The  purer  the  material  and  the  nearer  it  is  to  ferrite,  the  better 
will  be  its  electric  conductivity;  therefore  only  wrought  iron,  or 
the  softest  and  purest  forms  of  steel,  are  used  generally  for  wire 
for  electric  conduits.2  The  case  is  somewhat  complicated  when 

1 1  purposely  omit  here  the  consideration  of  such  hardness  as  that  pro- 
duced in  springs,  cutting  tools,  etc.,  by  heating  the  steel  to  a  bright-red  heat 
and  plunging  into  water,  as  this  will  be  discussed  in  Chapter  XIV. 

2  Omitting,  of  course,  the  use  of  copper,  which  is  not  under  consideration 
in  this  book,  but  which  is  probably  the  most  important  material  used  for 
electric  conductors. 


330  THE  METALLURGY  OF  IRON  AND  STEEL 

we  come  to  third  rails  for  electric  railroads,  which  have  now 
become  a  very  important  industrial  product,  because  so  pure  a 
material  will  be  very  soft  and  will  rapidly  wear  away  under  the 
abrasion  of  the  contact-shoes.  To  increase  the  hardness  of  these 
rails  with  the  least  decrease  in  electric  conductivity,  it  is  best  to 
avoid  nickel  and  manganese,  which  decrease  electric  conductivity 
in  greater  proportion  than  the  other  elements,  and  to  obtain  the 
hardness  as  much  as  possible  from  phosphorus,  and  not  from 
carbon,  because  phosphorus  will  give  the  greatest  amount  of  hard- 
ness with  the  least  decrease  in  the  purity  of  the  iron.  As  high 
phosphorus  steels  are  difficult  to  roll,  however,  the  section  of  the 
rail  chosen  should  be  as  free  as  possible  from  sharp  corners  and 
thin  flanges,  in  order  that  the  tearing  action  in  rolling  may  be  as 
slight  as  possible. 

MAGNETIC  PROPERTIES  OF  STEEL 

Alpha  ferrite  is  the  magnetic  constituent  of  iron  and  steel, 
and  therefore  the  greater  the  amount  of  this  constituent  present, 
the  greater  will  be  the  magnetic  force  and  magnetic  permeability 
of  the  material  and  the  less  its  magnetic  hysteresis.  On  this 
account  the  cores  of  electromagnets,  the  armatures  of  dynamos, 
etc.,  are  commonly  made  of  Swedish  wrought  iron,  which  is  the 
purest  commercial  form  of  iron  made.1 

Ferrite  has  no  permanent  magnetism,  but  immediately  loses 
its  magnetic  force  when  it  is  out  of  contact  with  a  magnet,  or,  in 
the  case  of  cores  of  electric  magnets,  when  the  electric  current  is 
cut  off.  Permanent  magnets  are  therefore  made  of  a  high-carbon 
steel  (1  per  cent.),  whose  strength  and  permanency  are  increased 
if  about  5  per  cent,  of  tungsten  is  present.  This  steel  is  heated 
above  the  critical  temperature  and  hardened  in  water,  after  which 
it  is  magnetized  by  causing  an  electric  current  to  flow  around  it  for 
a  short  time.  Steel  so  treated  will  retain  the  magnetic  force  for 
many  years.  Osmond  has  explained  the  permanent  magnetism 
of  steel  in  the  following  very  ingenious  manner:  Each  molecule 
of  alpha  ferrite  is  believed  to  have  a  north  and  a  south  magnetic 
pole,  which,  in  the  ordinary  unmagnetized  condition  of  the  iron, 

1  A  silicon  alloy  of  iron  with  a  double-heat  treatment  discovered  by  R.  A. 
Hadfield,  and  having  a  very  high  magnetic  force  and  permeability,  will  be 
discussed  under  the  head  of  "Alloy  Steels." 


THE  CONSTITUTION  OF  STEEL 


331 


will  be  oriented  in  many  different  directions,  as  shown  in  Fig.  255. 
When  this  piece  of  iron  is  placed  in  the  magnetic  field,  however, 
the  molecules  arrange  themselves  in  accordance  with  the  lines  of 
magnetic  force,  with  their  north  poles  all  in  one  direction  and 
their  south  poles  all  in  the  opposite  direction,  thus  making  the 
whole  piece  of  iron  a  magnet.  As  soon  as  the  magnetic  force  is 
removed,  however,  the  molecules  all  return  to  their  original 
orientation,  and  the  whole  piece  of  iron  loses  its  magnetism.  We 
have  already  learned  that  it  is  only  the  alpha  molecules  which  have 


FTG.  255. 


C»      Of      0      O   & 


£*    c*    <=» 


FIG.  256. 

north  and  south  magnetic  poles,  and  if  the  steel  consists  entirely 
of  beta  or  gamma  molecules,  it  is  not  capable  of  becoming  magnetic. 
According  to  Osmond's  theory,  when  steel  is  cooled  rapidly  from 
above  the  critical  temperature,  the  shortness  of  the  time  taken  in 
reaching  the  atmospheric  temperature  is  such  that  only  a  part 
of  the  molecules  are  able  to  change  to  the  alpha  allotropic  form, 
and  the  remainder  are  retained  in  the  gamma  form.  This  re- 
tention is  assisted  by  the  1  per  cent,  of  carbon  present,  which 
acts  as  a  brake  to  make  the  change  slower.  When,  now,  this 
hardened  steel  is  subjected  to  the  magnetic  force,  the  alpha 
molecules  orient  themselves  with  their  north  poles  all  in  one 
direction;  but  when  the  magnetic  force  is  removed  there  is  a 
certain  number  of  gamma  molecules  present  to  interfere  with  the 
free  movement  of  the  alpha  molecules  and  prevent  them  from 


332  THE  METALLURGY  OF   IRON  AND   STEEL 

returning  to  the  original  unoriented  position.  This  explanation 
implies  that  the  magnetic  force  is  sufficient  to  overcome  the 
resistance  of  the  gamma  molecules  and  force  the  alpha  molecules 
into  a  magnetic  position,  but  that  the  force  of  the  alpha  molecules 
tending  to  return  to  their  original  position  is  not  so  great. 

The  welding  of  steel  and  the  effect  of  different  elements  upon 
it  will  be  discussed  in  Chapter  XIV. 


REFERENCES  ON  THE  CONSTITUTION  OF  STEEL 

110.  F.  Osmond  and  G.  Cartaud.     "The  Crystallography  of  Iron/' 

Journal  Iron  and  Steel  Institute,  No.  Ill,  1906,  pages  444- 
492. 

111.  Albert  Sauveur.     "The  Constitution  of  Iron-Carbon  Alloys." 

Same  Journal,  No.  4,  1906,  pages  493-575. 

112.  J.   O.   Arnold   and   A.   A.   Read.     "Chemical   Relations   of 

Carbon  and  Iron."  Journal  of  the  Chemical  Society,  vol. 
Ixv,  page  788. 

113.  J.  O.  Arnold  and  G.  B.  Waterhouse.     "The  Influence  of 

Sulphur  and  Manganese  on  Steel."  Journal  Iron  and  Steel 
Institute,  No.  1,  1903,  pages  136-160. 

114.  J.  O.  Arnold.     "The  Influence  of  Elements  on  Iron."     Same 

Journal,  No.  1,  1894,  page  107. 

115.  J.  E.  Stead.     Same  Journal,  No.  11,  1900,  pages  60  et  seq.; 

and  also  Cleveland  Institution  of  Engineers,  September  6, 
1906. 

116.  Bradley  Stoughton.     "  Notes  on  the  Metallography  of  Steel." 

International  Engineering  Congress,  1894.  Transactions, 
American  Society  of  Civil  Engineers,  vol.  liv,  Part  E,  pages 
357-421. 

117.  Proceedings  of  the  American  Society  for  Testing  Materials, 

vol.  i,  1901;  vol.  vii,  1907.  Philadelphia.  This  society  is 
composed  of  representative  men  from  the  great  purchasers 
and  users  of  engineering  and  other  kinds  of  materials  in 
America,  from  the  manufacturers  and  of  representative 
scientific  men.  All  sides  of  the  question  are  usually  repre- 
sented in  the  discussions  of  this  society. 

118.  Proceedings    of    the    International    Association    for    Testing 

Materials.     Vienna,  Austria. 


XII 
THE  CONSTITUTION  OF  CAST  IRON 

PRACTICALLY  all  the  cast  iron  which  is  not  purified  is  used 
for  making  iron  castings,  so  that  a  study  of  the  constitution  of 
cast  iron  resolves  itself  into  a  study  of  iron  castings.  The  difference 
between  cast  iron  and  steel  is  that  the  former  contains  less  iron 
and  more  impurities,  especially  carbon,  silicon,  phosphorus,  and 
occasionally  sulphur  and  manganese.  The  advantages  of  cast 
iron,  and  the  reason  it  is  used  as  much  as  it  is,  are  its  fluidity, 
lesser  amount  of  shrinkage  when  cooling  from  the  molten  state, 
relative  freedom  from  checking  in  cooling,  and  the  ease  with  which 
very  different  properties  are  conferred  upon  it  at  will.  Its  dis- 
advantages are  its  weakness  and  lack  of  ductility  and  malleability. 
The  last-named  deficiency  renders  it  practically  impossible  to 
put  any  work  upon  cast  iron ;  hence  it  can  never  be  wrought  to 
shape  and  must  always  be  used  in  the  form  of  castings.  Its  most 
important  advantage  is  probably  its  ready  fusibility,  which  makes 
it  so  easy  to  melt  and  cast,  and  its  cheapness. 

Graphite.  —  All  of  the  characteristic  qualities  of  cast  iron  are 
due  to  the  presence  of  the  large  amount  of  impurities  in  it.  These 
impurities  are  the  same  in  kind  as  the  impurities  in  steel,  and 
differ  only  in  amount,  with  the  single  exception  of  graphite. 
This  constituent  is  almost  never  found  in  steel,  or  is  found  in 
such  a  very  small  number  of  cases,  and  those  cases  being  confined 
to  the  high-carbon  steels,  the  amount  of  which  is  very  small  in 
comparison,  that  we  may  almost  disregard  it.  In  cast  iron, 
however,  it  is  the  largest  and  one  of  the  most  important  con- 
stituents. It  occurs  in  thin  flakes,  in  sizes  varying  from  micro- 
scopic proportions  to  an  eighth  of  a  square  inch  in  area,1  dis- 
seminated through  the  body  of  the  metal  and  forming  an  intimate 

1  In  rare  and  unusual  cases  the  flakes  of  graphite  may  be  as  much  as  an 
inch  and  a  half  to  two  square  inches  in  area,  but  practically  never  so  large 
in  the  commercial  cast  irons. 

333 


334  THE  METALLURGY  OF   IRON  AND  STEEL 

mechanical  mixture,  a  magnified  section  of  which  is  shown  in 
Fig.  259.  Each  flake  of  graphite  is  composed  of  smaller  flakes, 
built  up  somewhat  like  the  sheets  of  mica  with  which  all  are 
familiar,  but  with  very  little  adhesion  between  the  small  com- 
ponent flakes,  so  that  the  sheet  of  graphite  may  be  split  apart  with 
very  little  force.  Graphite  is  very  light  in  weight,  having  a  specific 
gravity  of  only  about  2.25  as  compared  with  a  specific  gravity  of 
7.86  for  pure  iron;  consequently  although  the  percentage  of 
graphite  by  weight  is  only  4  per  cent,  or  less  of  the  iron,  its  per- 
centage by  volume  may  be,  in  normal  cases,  as  much  as  14  per 
cent.  This  may  readily  be  seen  by  noting  the  amount  of  space 
occupied  by  the  graphite  flakes  in  Fig.  263. 

Combined  Carbon.  —  We  have  already  discussed  the  solidifica- 
tion and  cooling  of  cast  iron,  and  it  will  be  remembered  that  all 
the  carbon  which  does  not  precipitate  as  graphite  forms  first 
as  austenite,  •  which  later  decomposes  into  ferrite  and  cementite. 
In  short,  all  the  carbon  in  cast  iron  will  ultimately  be  found  partly 
in  the  form  of  graphite  and  partly  in  the  form  of  cementite.  The 
carbon  of  cementite  in  cast  iron  commonly  goes  under  the  name 
of  '  combined  carbon/  but  it  must  be  remembered  that  cementite 
is  the  constituent  which  gives  the  observed  effects. 

White  Cast  Iron.  —  In  white  cast  iron  the  carbon,  amounting 
often  to  3  or  4  per  cent.,  will  all  be  in  the  form  of  cementite,  which 
will  therefore  form  45  to  60  per  cent,  of  the  material ;  consequently 
white  cast  iron  will  possess  largely  the  properties  of  cementite. 
It  is  very  hard  and  brittle,  being  machined  only  with  the  greatest 
difficulty  and  with  special  kinds  of  cutting  tools,  and  resisting 
wear  by  abrasion  very  effectively.  It  is  so  brittle  as  to  be  readily 
broken  by  the  blows  of  a  hammer,  and  is  weak  because  of  the 
presence  of  very  large  plates  of  cementite,  which  adhere  but 
slightly  to  one  another.  Consequently  white  cast  iron  has  few 
uses  and  is  employed  usually  only  as  a  hard  surface  on  the  outside 
of  gray-iron  castings. 

Gray  Cast  Iron.  —  Gray  cast  iron  will  have  about  the  same 
total  amount  of  impurities  present  as  white  cast  iron,  the  only 
difference  being  that  the  carbon  is  now  partly  or  wholly  pre- 
cipitated as  graphite.  The  gray  color  of  a  freshly  broken  fracture, 
from  which  this  material  receives  its  name,  is  due  altogether  to 
the  graphite  present,  for  this  constituent  is  so  weak  that  the 
iron  breaks  chiefly  through  its  crystals,  which  are  rent  asunder, 


THE  CONSTITUTION  OF  CAST  IRON  335 

leaving  one  part  sticking  to  each  side  of  the  fracture.  The  weak- 
ness of  gray  cast  iron  as  compared  with  steel  is  thus  readily 
understood,  since  there  is  but  a  small  proportion  of  metallic 
surface  to  be  broken  and  the  graphite  splits  so  easily.  An  inter- 
esting experiment  is  to  take  a  freshly  broken  surface  of  gray  pig 
iron  and  brush  one-half  of  it  for  some  time  with  a  stiff  brush. 
In  this  way  the  adhering  crystals  of  graphite  are  partially  removed 
and  we  get  a  surface  which  is  almost  as  white  as  the  fracture  of 
white  cast  iron.  This  shows  clearly  that  the  gray  color  is  due 
altogether  to  the  graphite  and  that  the  metallic  part  is  as  silvery 
white  as  iron  itself.  The  prevalence  of  the  gray  color  also  shows 
how  completely  fracture  takes  place  through  the  graphite  crystals. 
Gray  cast-iron  castings  are  by  far  the  more  important,  and 
the  study  of  their  constitution  is  the  chief  object  of  this  chapter. 
These  castings  usually  contain  2  per  cent,  or  more  of  graphite 
and  less  than  1 J  per  cent,  of  combined  carbon.  It  will  be  observed 
that  this  limit  of  combined  carbon  is  also  the  range  found  in  steel. 
Furthermore,  it  will  be  observed  that  the  graphite  is  not  a  chemical 
component  of  the  metallic  body,  but  is  mechanically  mingled  with 
it.  In  this  sense,  therefore,  we  may  consider  gray  cast  iron  as  a 
very  impure  steel,1  mechanically  mixed  with  graphite, and  upon  this 
reasoning  the  study  of  its  constitution  becomes  much  simpler,2 
as  we  may  study  first  the  properties  of  the  metallic  part,  and 
next  that  of  the  graphite,  and  so  be  able  to  foretell  to  some  extent 
the  properties  of  the  mixture.  Indeed,  the  properties  of  the 
metallic  part  are  already  understood  pretty  well  from  our  dis- 
cussion of  the  constitution  of  steel,  and  there  is  no  new  con- 
stituent or  new  condition  except  the  larger  amounts  of  silicon  and 
phosphorus,  which  are  of  minor  importance,  because  their  effect 
is  collectively  far  less  than  the  weakening  and  embrittling  effect 
of  the  graphite.  Even  though  we  had  a  very  pure  metallic 

1  The  silicon  in  gray  cast  iron  is  usually  between  0.75  per  cent,  and  3  per 
cent.,  or,  let  us  say,  ten  times  that  in  steel,  while  the  phosphorus  is  usually 
from  0.5  to  1.5  per  cent.,  or,  again,  about  ten  or  more  times  that  in  steel. 
The  sulphur  varies  greatly,  but  is  not  infrequently  as  high  as  0.15  to  0.2 
per  cent.     Manganese  is  an  exception  and  is  usually  no  higher  in  cast-iron 
castings  than  in  steel. 

2  This  theory  of  the  constitution,  which  meets  with   very  favorable  ac- 
ceptance in  many  quarters,  was  independently  evolved  by  J.  E.  Johnson,  Jr. 
(American  Machinist,  1900),  and  H.  M.  Howe  (Trans.  A.  I.  M.  E.,  1901, 
vol.  xxxi,  pp.  318-339). 


336  THE  METALLURGY  OF  IRON  AND  STEEL 

constituent,  the  strength  and  ductility  of  this  portion  would  not 
be  sufficient  to  prevent  the  mass  as  a  whole  breaking  at  a  small 
load  and  without  exhibiting  any  practical  ductility,  because  of 
the  weakening  effect  of  the  crystals  of  graphite.  In  other  words, 
it  is  the  carbon  which  is  the  great  factor  in  determining  the 
properties  of  cast  iron,  for  this  may  be  either  all  graphitic,  or  all 
combined,  or  part  in  both  conditions. 

Effect  of  Temperature.  —  By  running  the  blast  furnace  very 
hot,  we  may  extend  the  saturation  point  of  the  iron  for  carbon 
and  thus  get  a  slightly  higher  total  carbon.  This  is  not  a  very 
potent  influence,  however,  for  we  seldom  have  total  carbon  more 
than  4.5  per  cent.,  or  less  than  3.25  per  cent.  This  control,  such 
as  it  is,  may  be  exercised  either  during  the  manufacture  of  the 
pig  iron  or  during  the  remelting  in  the  cupola,  because  in  the 
latter  furnace  the  liquid  iron  is  in  contact  with  coke  and  will 
absorb  carbon  up  to  its  saturation  point  at  the  existing  temperature. 

Rate  of  Cooling.  —  A  far  more  potent  influence,  however,  is  the 
transfer  of  carbon  from  the  graphitic  into  the  combined  form, 
or  vice  versa,  by  rapid  or  by  slow  cooling  from  the  molten  con- 
dition. It  will  be  remembered  that  the  carbon  is  always  dissolved 
in  the  iron  when  the  mass  is  in  a  molten  condition,  that  is,  when 
it  is  above  the  lines  A  B  and  B  C  in  Fig.  246.  As  we  cool  from 
the  molten  state,  graphite  precipitates,  but  this  cooling  must  be 
very  slow  indeed  for  this  normal  chemical  change  to  take  place 
completely  since  it  is  a  very  sluggish  change  and  requires  several 
seconds  for  its  accomplishment.  If,  therefore,  we  cool  with  great 
rapidity,  as,  for  example,  by  pouring  the  iron  into  a  metallic  mold 
which  '  chills '  it,  or  by  some  other  form  of  artificial  rapid  cooling, 
we  may  prevent  the  precipitation  of  graphite  by  denying  the  time 
necessary  for  the  chemical  reaction,  and  obtain  a  metal  in  which 
all  the  carbon  is  in  the  combined  form,  i.  e.,  white  cast  iron.  It  is 
also  evident  that,  by  a  rate  of  cooling  intermediate  between  this 
rapid  rate  and  the  slow  rate  which  permits  the  precipitation  of 
the  normal  amount  of  graphite,  we  may  obtain  an  intermediate 
amount  of  carbon  in  the  graphitic  form.  This  variation  in  the 
speed  of  solidification  is  a  very  important  means  of  producing 
combined  carbon  and  is  employed  very  largely  in  the  'chilling7 
of  the  surfaces  of  gray-iron  castings,  whereby  we  may  have  a 
relatively  soft  gray  iron  in  the  interior  of  each  article  and  a  hard 
surface  extending  to  almost  any  desired  depth.  For  example, 


THE  CONSTITUTION  OF  CAST  IRON  337 

chilled-iron  rolls  are  made  in  this  way  (see  page  201),  and  also 
American  railroad  car  wheels  l  which  are  cast  against  an  iron 
chill  (see  page  337),  giving  nearly  an  inch  depth  of  white  iron 
around  the  tread  and  flange  where  the  metal  is  to  suffer  abrasion 
in  grinding  over  the  rails,  while  the  web  and  bore  will  be  of  gray 
cast  iron,  because  cooled  more  slowly  in  the  sand  part  of  the 
mold,  and  thus  will  be  less  brittle  and  better  able  to  withstand 
the  shocks  of  service  and  machining. 

THE  EFFECT  OF  CARBON  ON  CAST  IRON 

The  nature  and  constitution  of  gray  cast  iron  is  far  more 
difficult  to  understand  than  that  of  steel,  and  even  greater  is  the 
difficulty  of  predicting  the  effect  of  any  change  in  composition  or 
in  constituents.  The  chief  reason  for  this  complexity  is  that  a 
change  in  any  one  of  the  constituents  of  gray  cast  iron  is  liable 
to  effect  changes  in  several  others  as  well.  The  simplest  example 
of  this  is  in  the  case  of  the  carbon;  we  have  total  carbon,  graphite, 
and  combined  carbon,  and  if  we  change  any  one  of  these  three, 
we  must  change  either  one  or  both  of  the  other  two,  and  it  makes 
a  great  deal  of  difference  which.  Indeed,  we  almost  never  change 
the  amount  of  graphite  without  making  the  reverse  change  in  the 
amount  of  combined  carbon,  and  vice  versa.  Thus  a  very  loose 
system  of  speaking  of  these  matters  has  come  into  vogue  among 
foundrymen.  For  instance,  it  is  very  common  to  hear  a  foundry- 
man  say:  'In  order  to  soften  your  iron,  increase  the  graphite'; 
but  what  he  really  means  is :  'In  order  to  soften  your  iron,  decrease 
the  combined  carbon.'  He  knows  that  the  one  change  usually 
follows  from  the  other,  and  he  speaks  of  it  in  this  way,  regardless 
of  the  fact  that  graphite  can  be  increased  (i.  e.,  by  increasing 
the  total  carbon  and  leaving  the  combined  carbon  the  same  or 
a  dittle  higher) ,  and  yet  the  iron  will  not  be  made  any  softer,  but 
may  .even  be  harder. 

Graphite  and  Shrinkage.  —  The  most  important  effect  of 
graphite  on  cast  iron,  aside  from  causing  weakness,  is  in  decreasing 

JIn  other  important  railroad  countries  it  is  more  usual  to  have  the  car 
wheels  made  of  steel,  as  it  is  believed  that  the  iron  wheels  are  not  sufficiently 
strong  and  ductile.  The  manufacture  of  pressed-steel  car  wheels  is  increasing 
in  America;  nevertheless,  the  chilled  cast-iron  wheels  seem  to  give  very  good 
service. 


338  THE  METALLURGY  OF   IRON  AND   STEEL 

the  shrinkage.  The  reason  for  this  will  be  understood  when  we 
consider  what  happens  when  cast  iron  solidifies.  It  will  be 
remembered  that  when  the  eutectic  forms,  the  cast  iron  breaks  up 
into  alternate  plates  of  graphite  and  austenite.  This  separation 
of  graphite  from  solution  is  the  birth  of  a  new  constituent,  and 
this  constituent  occupies  space,  so  that  there  is  an  expansion  of 
the  mass  as  a  whole  in  proportion  to  the  amount  of  graphite  that 
separates.  If,  therefore,  we  pour  liquid  cast  iron  into  a  mold, 
which  is,  of  course,  entirely  filled  at  the  moment  when  the  iron 
begins  to  solidify,  the  first  action  that  takes  place  after  the  begin- 
ning of  solidification  is  an  expansion,  due  to  the  separation  of 
graphite.  The  expansion  continues  for  several  moments  until 
the  chemical  precipitation  is  completed,  after  which  the  metal 
begins  to  contract,  as  all  metals  do  in  cooling  from  a  high  tempera- 
ture; but  the  preliminary  expansion  has  been  so  great  that  the 
ultimate  shrinkage  may  be  only  about  one-half  what  it  otherwise 
would  have  been.  We  can  thus  control  this  shrinkage  by  con- 
trolling the  amount  of  the  expansion,  through  varying  the  graphite. 
This  point  will  be  more  readily  understood  by  referring  to  Fig.  257r 
which  is  taken  from  a  recent  article  by  Prof.  Thomas  Turner  of 
England.1 

Explanation  of  Fig.  257.  —  The  point  0  marks  the  position 
occupied  by  the  end  of  the  bars  at  the  moment  of  solidification. 
It  will  be  seen  that  in  the  case  of  copper  the  metal  contracts  con- 
tinuously from  this  point,  as  shown  by  the  continuous  drop  of  the 
curve.  In  the  case  of  white  cast  iron,  the  metal  contracts  con- 
tinuously until  we  reach  a  certain  point  (which  is  at  a  temperature 
of  about  665°  C.) ,  when  a  momentary  arrest  of  the  shrinkage  takes 
place,  after  which  the  metal  again  contracts.  This  arrest  is 
common  to  all  cast  iron  and  steel  and  marks  the  decomposition  of 
austenite  at  the  point  S,  Fig.  246,  page  314.  Now,  see  what  a 
difference  there  is  in  the  case  of  gray  cast  iron,  which  does  not 
shrink  immediately  after  freezing,  but  expands  very  appreciably, 
as  shown  by  he  rise  in  the  curve.  This  expansion  is  due  to  the 
graphite  that  is  being  expelled  from  the  metal  and  occupies  space 
between  the  particles  of  iron. 

Again,  in  the  case  of  the  Northampton  iron,  which  is  high  in 
both  graphite  and  phosphorus,  the  expansion  is  very  long-con- 
tinued, and  the  metal  cools  to  almost  a  black  heat  before  the 
1  Journal  of  the  Iron  and  Steel  Institute,  No.  1,  1906,  page  57. 


THE  CONSTITUTION  OF  CAST   IRON 


339 


bar  has  shrunk  again  to  the  size  it  had  when  first  cast.  This 
expansion  is  again  due  to  the  separation  of  carbon,  and  is  assisted 
apparently  by  the  phosphorus  keeping  the  iron  in  a  semifluid 
condition  for  a  long  time  and  thus  allowing  the  graphite  more 
easily  to  separate  and  make  place  for  itself.  Here,  too,  we  have 
an  explanation  why  phosphoriferous  irons  fill  every  crevice  of 


FIG.   257.  —  SHRINKAGE  CURVES. 

the  molds  so  perfectly.  Being  in  a  pasty  condition  for  some 
time,  and  continually  expanding,  the  semifluid  metal  is  forced 
into  the  tiniest  crevices  of  the  molds,  filling  all  the  corners  with 
astonishing  sharpness. 

It  is  evident  that  any  increase  in  graphite,  whether  caused 
by  an  increase  in  total  carbon  or  by  a  decrease  in  combined  carbon, 
will  produce  less  shrinkage.  The  extent  of  this  may  be  judged  by 
noting  that  gray  cast  iron  expands  so  much  in  solidifying  that  no 
contraction  cavity  or  pipe  is  formed,  such  as  occurs  in  the  case  of 


340  THE  METALLURGY  OF   IRON  AND  STEEL 

steel.  If  the  iron  is  only  slightly  gray,  or  if  it  is  a  very  large 
section  of  metal,  then  a  slight  spongy  place  may  be  formed  in  the 
center,  which  is  the  nearest  approach  to  a  shrinkage  cavity  that 
is  normally  found  in  most  iron  castings. 

Graphite  and  Porosity.  —  It  is  also  evident  that  an  increase 
in  graphite,  whether  produced  by  an  increase  in  total  carbon  or 
by  a  decrease  in  combined  carbon,  will  increase  the  porosity  of 
the  casting,  which  is  often  disadvantageous,  as  in  the  case  of 
hydraulic  cylinders  or  other  receptacles  for  holding  liquids  under 
pressure.  The  separation  of  much  graphite  usually  is  accompanied 
by  large-sized  graphite  crystals,  and  therefore  the  crystals  of 
the  mass,  as  revealed  by  the  fracture,  appear  large  and  the  grain 
is  said  to  be  'open/ 

Graphite  and  Workability.  —  When  we  come  to  consider  the 
effect  of  graphite  upon  the  softness  or  workability  of  the  cast 
iron,  it  is  evident  that  we  must  consider  it  in  relation  to  other 
things;  for  if  we  increase  the  graphite  by  increasing  the  total 
carbon,  then  we  increase  the  workability  of  the  metal  only  in  so 
far  as  the  graphite  acts  as  a  lubricant  for  the  tool  that  is  doing 
the  cutting.  Evidently  the  tool  will  have  no  difficulty  in  cutting 
through  the  soft  flakes  of  graphite;  the  chief  resistance  to  it  will 
be  given  by  the  metallic  part  of  the  mixture.  Though  the  lubricat- 
ing effect  of  the  graphite  undoubtedly  helps  the  tool,  its  presence 
evidently  cannot  increase  the  actual  softness  of  the  metallic 
body  with  which  it  is  mixed.  But,  on  the  other  hand,  if  we 
increase  the  graphite  by  decreasing  the  combined  carbon,  then 
we  have  not  only  increased  the  amount  of  lubricant,  but  we  have, 
in  addition,  increased  the  softness  of  the  metallic  part  of  the 
mixture  by  reducing  the  proportion  of  cementite,  which  is  the 
hardener,  in  it. 

Graphite  and  Strength.  —  Everything  else  being  equal,  it  is 
evident  that  the  more  graphite  we  have  in  cast  iron,  the  weaker 
it  will  be,  for  we  have  already  shown  that  gray  cast  iron  breaks 
by  the  ready  splitting  apart  of  the  flakes  of  graphite.  Thus,  if 
we  make  no  change  in  the  combined  carbon,  but  increase  the  total 
carbon  of  our  castings,  and  consequently  the  graphite,  we  should 
expect  a  corresponding  decrease  in  strength,  and  this  is  in  fact 
found  to  occur.  When,  however,  we  increase  the  graphite  and  at 
the  same  time  decrease  the  combined  carbon,  we  may  or  may  not 
get  an  increase  in  strength,  this  depending  altogether  on  how 


THE  CONSTITUTION   OF  CAST   IRON  341 

much  combined  carbon  there  was  before  and  after  the  change. 
For  example,  if  we  had  3  per  cent,  of  combined  carbon  and  1  per 
cent,  of  graphite  in  a  casting  that  casting  would  be  weak  be- 
cause of  too  high  combined  carbon.  To  decrease  this  and  in- 
crease the  graphite  would  have  a  beneficial  effect  on  strength. 
On  the  other  hand,  if  we  had  1  per  cent,  of  combined  carbon 
and  3  per  cent,  of  graphite,  to  decrease  the  combined  carbon 
and  increase  the  graphite  would  have  a  detrimental  effect  on 
strength.  We  must  therefore  consider  the  question  of  strength 
from  a  much  larger  viewpoint  than  by  considering  any  one  con- 
stituent alone. 

Combined  Carbon  and  Shrinkage.  —  Combined  carbon  has  very 
little  effect  on  the  shrinkage  of  cast  iron  except  in  so  far  as  it 
changes  the  graphite.  That  is  to  say,  if  by  increasing  the  com- 
bined carbon  we  decrease  the  graphite,  we  will  get  an  increase  in 
shrinkage,  and  vice  versa. 

THE   EFFECT   OF   SILICON,   SULPHUR,   PHOSPHORUS,   AND 
MANGANESE  ON  PIG  IRON 

The  constitution  of  cast  iron  is,  furthermore,  very  complicated 
because  of  the  double  influence  of  silicon,  sulphur,  phosphorus, 
and  manganese,  Each  of  these  elements  has  a  direct  influence 
upon  the  properties  of  the  material,  which  is  in  general  similar  to 
its  influence  upon  steel.  For  example,  silicon  produces  freedom 
from  oxides  and  blow-holes  and  makes  the  iron  more  fluid ;  man- 
ganese counteracts  the  effect  of  sulphur  and  increases  the  difficulty 
of  machining  the  material;  sulphur  makes  the  metal  very  tender 
at  a  red  heat,  and  therefore  liable  to  checking  if  put  under  strain 
during  this  period.  For  example,  if  a  casting  in  shrinking  tends 
to  crush  the  sand,  this  strain  will  be  more  liable  to  break  it  in  case 
the  sulphur  is  high.  Sulphur  also  makes  solidification  take  place 
more  rapidly,  and  causes  blow-holes  and  dirty  iron.  Phosphorus 
makes  the  metal  very  fluid  and  reduces  its  melting-point.  It  also 
makes  it  more  brittle  under  shock,  especially  when  cold,  and 
produces  a  fusible  eutectic,  a  photomicrograph  of  which  is  shown 
in  Fig.  253.  Phosphorus  and  sulphur  increase  the  tendency  to 
segregate. 

Furthermore,  the  various  compounds  of  the  impurities  with 
iron  and  with  each  other,  which  we  find  in  steel,  are  also  found  in 


342  THE  METALLURGY  OF   IRON  AND  STEEL 

cast  iron.  Indeed,  some  of  them  are  far  more  important  in  the 
latter  than  in  the  former,  because  the  amount  of  the  impurities  is 
greater.  This  is  especially  true  of  manganese  sulphide  and  iron 
sulphide,  for  the  sulphur  in  cast  iron  is  often  large  in  amount, 
while  the  manganese  is  often  intentionally  small  on  account  of  the 
difficulty  which  this  element  produces  in  the  machining  of  the 
casting.  Therefore  we  are  even  more  liable  to  find  iron  sulphide 
in  cast  iron  than  in  steel. 

But  the  direct  effect  of  these  impurities  is  usually  far  less 
important  than  their  indirect  effect,  namely,  their  influence  upon 
the  carbon.  After  all,  it  is  the  carbon  which  is  the  chief  factor  in 
controlling  the  most  important  properties  of  the  cast  iron,  and 
we  may  vary  this  either  by  increasing  or  decreasing  the  total 
amount,  or  else  leaving  the  total  amount  the  same,  by  increasing 
the  graphite  and  decreasing  the  combined  carbon,  or  vice  versa. 
It  is  the  ease  with  which  we  may  vary  the  amount  or  the  condition 
of  the  carbon,  and  therefore  the  properties  of  the  iron,  that  is  one 
of  the  most  important  advantages  of  the  material.  But  strangely 
enough,  although  it  is  easy  to  keep  this  control,  it  can  never 
be  accomplished  in  a  direct  way.  It  will  be  remembered  (see 
pages  35  to  38),  that  the  blast-furnace  manager  can  vary  the 
amount  of  silicon  and  sulphur  in  his  pig  iron  at  will;  that  he 
has  only  a  small  control  over  the  manganese  and  practically 
none  over  the  phosphorus  or  carbon,  but  that  the  metal  al- 
ways saturates  itself  with  this  latter  element;  and  it  has  also 
been  seen  (see  page  306)  that  the  limit  of  this  saturation  is 
small. 

Silicon.  —  By  means  of  his  control  over  the  silicon  and  sulphur, 
the  metallurgist  exercises  indirectly  his  most  important  control 
over  the  condition  of  the  carbon;  for  silicon  acts  as  a  precipitant 
of  carbon,  driving  it  out  of  combination  and  into  the  graphitic  form, 
so  that  with  about  3  per  cent,  of  silicon,  slow  cooling  and  very 
low  sulphur  and  manganese,  we  may  obtain  a  cast  iron  in  which 
almost  none  of  the  carbon  is  in  the  form  of  cementite.  That  is  to 
say,  the  presence  of  this  amount  of  silicon  acts  so  strongly  that 
it  may  partially  prevent  the  formation  of  austenite  during  solidifica- 
tion, and  also  cause  graphite  to  precipitate  instead  of  cementite 
at  690°  C.  (1275°  F.)  when  the  eutectoid  decomposes  (point 
S,  Fig.  246,  page  314),  so  that  it  decomposes  into  ferrite  and 
graphite  instead  of  ferrite  and  cementite.  The  maximum  pre- 


THE  CONSTITUTION  OF  CAST  IRON 


343 


cipitation  of  graphite  seems  to  occur  with  about  2.5  to  3.5  per 
cent,  of  silicon.  With  each  increase  of  silicon  up  to  that  point 
(the  amount  of  sulphur,  the  rate  of  cooling  and  other  influential 
conditions  remaining  the  same),  we  get  an  increase  in  the  amount 
of  graphite  precipitation,  but  when  the  amount  of  silicon  exceeds 
about  3  per  cent,  it  seems  to  reverse  its  effect,  and  each  addition 
of  silicon  thereafter  causes  an  increase  in  the  proportion,  not  of 
graphite,  but  of  combined  carbon.  At  this  point  large  amounts 
of  various  iron  silicides  (Fe2  Si,  Fe2  Sia,  etc.),  make  their  appearance. 
Then  the  color  of  a  freshly  broken  fracture  begins  to  be  bright 
like  a  mirror,  in  contradistinction  to  the  white  color  of  ordinary 
white  cast  iron,  which  has  more  nearly  the  appearance  of  frosted 
silver. 

Sulphur.  —  The  influence  of  sulphur  upon  the  formation  of 
graphite  is  almost  the  exact  opposite  of  the  influence  of  silicon. 
That  is  to  say,  each  increase  in  the  amount  of  sulphur  present 
increases  the  amount  of  combined  carbon  in  the  iron.  It  is 
usually  considered  that  each  0.01  per  cent,  of  sulphur  will  neu- 
tralize fifteen  times  as  much  silicon  (i.e.,  0.15  per  cent.)  in  its 
effect  upon  the  condition  of  the  carbon  in  the  iron.  It  is  also 
very  important  to  note  that  when  the  sulphur  is  in  the  form 
of  MnS,  it  is  not  so  potent  in  increasing  the  combined  carbon 
as  when  it  is  in  the  form  of  FeS.  An  interesting  example  of 
this  is  shown  in  the  analysis  of  the  two  railroad  car  wheels 
given  below: 


Fe 

Total 
Carbon 

Si 

Mn 

P 

S 

Graph- 
ite 

C.C. 

Good  wheel  
Poor  wheel  

94.79 
95.00 

3.84 
3.52 

0.69 
0.65 

0.13 
0.12 

0.43 
0.52 

0.12 
0.19 

3.30 
2.35 

0.54 
1.17 

Good  wheel  required  150  blows  of  25-lb.  sledge  to  break  it.     Poor  wheel 
required  8  blows  of  25-lb.  sledge  to  break  it. 

It  will  be  observed  that  the  poor  wheel  has  more  than  twice  as 
much  combined  carbon  as  the  good  wheel,  although  the  sulphur 
in  the  poor  wheel  is  only  about  50  per  cent,  more  than  the  sulphur 
in  the  good  wheel,  the  other  impurities  being  nearly  the  same. 
When  we  come  to  figure  out  the  amount  of  MnS  and  FeS  in  the 
two  wheels,  we  find,  however,  the  explanation  of  the  large  amount 
of  combined  carbon  in  the  poor  wheel.  We  also  have  an  ex- 


344 


THE  METALLURGY  OF   IKON  AND   STEEL 


planation  of  the  poor  quality  of  this  wheel  in  the  increased  amount 
of  FeS  present. 


CONSTITUENT 

Good  Wheel 
Per  Cent. 

Bad  Wheel 
Per  Cent. 

MnS   . 

0.206 

0.195 

FeS     

0.121 

0.315 

FeSi 

2  045 

1  923 

Fe3P                                          .            ... 

2  755 

3  335 

Pearlite               .          

67  610 

84  492 

Ferrite     

23.963 

0  000 

Cementite  

0.000 

7  390 

Graphite 

3  300 

2  350 

Totals  

100  000 

100  000 

Manganese.  —  Manganese  increases  the  total  carbon  in  pig 
iron.  Manganese  also  increases  the  proportion  of  the  carbon  that 
is  in  the  combined  form,  but  its  influence  in  this  respect  is  far 
less  than  that  of  the  sulphur;  moreover,  the  statement  requires 
the  following  qualification:  as  much  manganese  as  is  combined 
with  sulphur  in  the  form  of  MnS  does  not  increase  the  proportion 
of  carbon  in  the  combined  form.  Indeed,  it  has  really  the  reverse 
effect,  because  it  takes  the  sulphur  out  of  the  form  of  FeS,  in 
which  it  is  most  powerful  in  increasing  the  combined  carbon.  In 
this  sense  therefore,  the  manganese  actually  decreases  the  amount 
of  combined  carbon. 

The  excess  manganese  over  that  necessary  to  form  MnS  (that 
is,  the  manganese  in  the  form  of  [FeMn]3C)  increases  the  propor- 
tion of  carbon  in  the  combined  form,  and  also  increases  the  amount 
of  total  carbon  even  more  potently  than  does  the  manganese, 
which  is  in  the  form  of  MnS.  We  therefore  have  a  strange  con- 
tradiction, in  that  when  the  manganese  is  high  an  increase  in 
sulphur  will,  by  decreasing  the  amount  of  (FeMn)3C,  actually 
decrease  the  tendency  of  manganese  to  raise  the  total  carbon  as 
well  as  the  combined  carbon.  To  sum  up,  manganese  and  sulphur 
both  tend  to  increase  the  total  carbon  and  the  combined  carbon, 
and  yet  they  neutralize  each  other  in  this  respect. 

Phosphorus.  —  The  effect  of  phosphorus  upon  the  carbon  is 
somewhat  self-contradictory:  from  a  chemical  standpoint  it.  tends 
to  increase  the  proportion  of  combined  carbon,  and  this  is  es- 
pecially true  when  the  silicon  is  low  and  the  phosphorus  high 
(say  above  1.25  per  cent,).  But  phosphorus  also  has  the  effect  of 


THE  CONSTITUTION  OF  CAST   IRON  345 

lengthening  the  period  of  solidification.  That  is  to  say,  it  makes 
the  iron  pass  through  a  somewhat  mushy  stage  of  solidification, 
and  this  mushy  stage  lasts  for  several  minutes.  This  lengthening 
of  the  solidification  period  gives  a  longer  time  in  which  graphite 
can  precipitate.  Therefore,  when  the  silicon  is  relatively  high 
(at  least  over  1  per  cent.),  and  there  is  consequently  a  strong 
tendency  for  graphite  to  precipitate  during  solidification,  this 
precipitation  is  actually  aided  by  the  phosphorus,  and  the  graphite 
occurs  not  only  more  abundantly,  but  in  larger-sized  flakes.  When, 
however,  the  amount  of  phosphorus  is  very  large,  its  chemical 
effect  is  great  enough  to  retain  the  carbon  in  the  combined  form, 
in  spite  of  the  long  period  of  solidification.  We  may  sum  this  up 
by  saying  that  if  the  chemical  conditions  are  such  that  graphite 
is  bound  to  precipitate,  then  the  physical  effect  of  the  phosphorus 
makes  this  precipitation  the  more  easy;  but  if  there  is  enough 
phosphorus  present  to  produce  a  strong  chemical  effect  of  its  own, 
or  if  the  other  chemical  influence  is  not  very  powerful  (i.e.,  if 
the  silicon  is  low),  then  phosphorus  tends  to  keep  the  carbon  in  the 
combined  form. 


THE  PROPERTIES  OF  CAST  IRON 

Let  us  now  consider  the  properties  of  cast  iron,  and  sum- 
marize under  the  head  of  each  the  influence  of  the  various  elements 
and  conditions  upon  them. 

Shrinkage.  —  The  shrinkage  of  cast  iron  is  of  more  importance 
than  might  at  first  appear,  because  the  greater  it  is  the  greater 
will  be  the  strains  set  up  in  the  cooling  of  the  casting,  and  con- 
sequently the  liability  to  check;  also,  the  greater  will  be  the 
allowance  necessary  in  order  that  the  casting  may  be  true  to  the 
size  called  for  by  the  drawings.  Graphite  is  the  most  important 
impurity  in  this  connection,  because  of  the  expansion  which  its 
separation  causes.  This  separation  should  take  place  at  the 
moment  of  solidification,  but  is  usually  not  complete  then,  and 
therefore  the  precipitation  continues  during  the  fall  of  the  temper- 
ature to  several  degrees  delow  the  freezing-point.  Furthermore, 
when  the  silicon  is  high,  graphite  instead  of  cementite  separates 
at  the  lower  critical  point  (i.e.,  the  line  P  S  K  in  Fig.  246,  page  314). 
As  silicon  and  the  rate  of  cooling  are  the  chief  influences  which 
control  the  separation  of  graphite,  they  become  the  governing 


346 


THE  METALLURGY  OF   IRON  AND   STEEL 


factors  in  the  shrinkage  of  the  iron.  Indeed,  when  sulphur  is 
practically  normal  and  no  other  unusual  conditions  prevail,  there 
is  such  a  close  relation  between  the  size  of  the  castings  1  and  the 
percentage  of  silicon  on  the  one  hand,  and  the  amount  of  shrinkage 
on  the  other  hand,  that  any  one  of  the  three  may  be  calculated 
when  the  other  two  are  known  (see  Table  XXVII) . 

TABLE  XXVII.— RELATION  OF  SHRINKAGE  TO  SIZE  AND 
PERCENTAGE  OF   SILICON 


PER 

CENT. 

^in. 

1  in. 

2  in.  X 

2  in. 

3  in. 

4  in. 

OP 

SILICON 

square 

square 

lin. 

square 

square 

square 

Perpendicular      readings 
show    decrease  due  to 

increase  in  silicon. 

1.00 

.183 

.158 

.146 

.130 

.113 

.102 

1.50 

.171 

.145 

.133 

.117 

.098 

.087 

2.00 
2.50 

.159 
.147 

.133 
.121 

.121 

.108 

.104 
.092 

.085 
.073 

.074 
.060 

Horizontal  readings  show 
decrease    of    shrinkage 

3.00 

.135 

.108 

.095 

.077 

.059 

.045 

due  to  size. 

3.50 

.123 

.095 

.082 

.065 

.046 

.032 

Sulphur  is  important  in  this  connection,  and  its  effect  is  con- 
trary to  that  of  silicon,  because  of  its  tendency  to  retain  the  carbon 
in  the  combined  form.  Manganese  and  phosphorus  each  has  a 
less  important  influence.  Manganese,  by  increasing  the  total  car- 
bon, tends  to  increase  graphite  and  therefore  decrease  shrink- 
age. So  far  as  it  neutralizes  sulphur,  moreover,  its  effect  is  in  the 
same  direction.  Phosphorus  decreases  shrinkage,  both  because  it 
contributes  to  the  fluidity,  of  the  metal  and  therefore  gives  a  better 
opportunity  for  carbon  to  separate,  and  also  because  of  the  ex- 
pansion caused  when  the  phosphorus  eutectic  separates  from 
solution.  A  hotter  casting  temperature  of  the  iron  has  the  effect 
of  delaying  solidification  by  heating  up  the  mold,  so  that  graphite 
has  a  little  more  chance  to  separate.  This  effect  is  noticed  but 
slightly  amidst  the  other  conditions. 

A  table  showing  the  relation  between  the  size  of  the  casting, 
the  amount  of  silicon,  and  the  shrinkage  is  given  above  and  is 
taken  from  page  155  of  No.  93.  Slight  changes  must  be  made  in 
this  table  by  each  foundry  for  the  conditions  of  sulphur,  phos- 
phorus, temperature,  etc.,  obtaining  there;  but  those  given 
herewith  will  be  found  sufficiently  accurate  for  all  ordinary  pur- 
poses where  conditions  are  anywhere  near  normal. 

1  Which  is  the  chief  influential  feature  in  the  rate  of  cooling. 


THE  CONSTITUTION  OF  CAST  IRON 


347 


Shrinkage  Tests.  —  At  many  foundries  it  is  the  custom  to 
make  a  shrinkage  test  of  the  iron  from  each  cupola  at  least  once 
a  day.  The  simplest  way  of  making  these  tests  is  to  pour  into  a 
mold  12  in.  long,  with  a  sectional  area  approximately  proportionate 
to  the  size  of  the  castings  made,  some  of  the  iron  from  about  the 
middle  of  the  cupola  run.  The  casting  must  be  poured  flat,  and 
the  difference  between  12  in.  and  the  length  of  the  cold  bar  is  the 
shrinkage  of  the  metal.  This  method  is  somewhat  crude  and, 
although  it  gives  valuable  results,  has  been  greatly  improved  by 
W.  J.  Keep  1  and  Prof.  T.  Turner,2  who  have  devised  simple  and 
inexpensive  pieces  of  apparatus  whereby  the  iron,  after  it  begins 
its  solidification,  draws  a  curve  showing  first  the  expansion  and 
later  the  contraction.  It  is  by  means  of  Professor  Turner's  ap- 
paratus that  the  curves  shown  in  Fig.  257,  page  339,  were  made. 
With  very  little  care  these  curves  can  be  obtained  to  show  with 
sufficient  accuracy  for  all  ordinary  purposes  the  percentage  of 
graphite  and  also  (other  conditions  being  normal,  or  nearly  so), 
the  percentages  of  silicon  and  combined  carbon,  and  the  strength, 
hardness,  and  porosity.  Indeed  the  curves  are  more  useful  than 
many  single  tests,  because  they  show  at  a  glance  the  net  effect 
of  several  varying  conditions. 

Density.  —  The  maximum  density  of  cast  iron  occurs  with 
about  1  per  cent,  of  silicon.  With  less  than  that,  the  iron  is  liable 
to  contain  spongy  spots,  due  to  high  shrinkage  on  account  of  low 
graphite.  With  more  silicon  the  separation  of  graphite  decreases 
density.  Above  2  per  cent,  of  silicon,  the  grain  of  the  iron  becomes 
so  open  as  to  be  actually  porous  and  the  density  falls  off  by  12 
per  cent. 

TABLE   OF  DENSITIES 


Specific 
Gravity 

Weight  per 
Cubic  Foot 

Pure  iron         

7.86 

490 

White  east  iron  

7.60 

474 

Mottled  cast  iron 

7  35 

458 

Light  pray  cast  iron  

7.20 

450 

Dark  gray  cast  iron  

6.80 

425 

Sample  of  gray  cast  iron  when  cold             ...    . 

7  17 

448 

Same,  when  liquid  

6.65 

416 

See  Chapter  XX  of  No.  93,  page  291. 


Reference  on  page  338. 


348  THE  METALLURGY  OF  IRON   AND   STEEL 

To  make  a  close-grained  iron  for  hydraulic  work  the  sulphur 
should  be  from  0.03  to  0.055  per  cent.  If  more  than  this,  the  iron 
is  liable  to  be  dirty,  to  contain  spongy  spots  on  account  of  low 
graphite,  to  be  difficult  to  machine  on  account  of  high  combined 
carbon,  and  to  be  weak,  because  high  sulphur,  aside  from  its  effect 
on  carbon,  reduces  the  strength.  Especially,  if  the  phosphorus  is 
high  must  the  sulphur  be  kept  down  to  these  limits,  or  the  iron 
will  be  hard,  brittle,  and  weak. 

There  should  be  from  0.4  to  0.6  per  cent,  of  manganese.  We 
do  not  want  more  manganese  than  this,  or  the  casting  will  be 
difficult  to  machine.  We  do  not  want  less  than  I  have  indicated, 
because  manganese  assists  in  counteracting  the  bad  effects  of 
sulphur  and  phosphorus. 

Phosphorus  has  a  double-acting  influence  on  the  porosity  of 
cast  iron:  (1)  It  increases  the  size  of  the  crystals,  decreases  shrink- 
age and  causes  a  large  expansion  after  solidification,  as  explained 
in  connection  with  Fig.  257;  but  (2)  it  fills  all  the  crevices  between 
the  crystals  and  in  the  interior  of  the  iron,  which,  by  decreasing 
the  porosity,  counteracts  its  first  influence.  When  the  phosphorus 
is  high,  the  phosphorus  and  iron  form  a  eutectic,  which  remains 
fluid  for  a  long  time  and  fills  the  tiniest  crevices  in  the  interior  of 
the  metal.  For  this  reason  iron  for  hydraulic  work  may  run 
up  to  0.7  per  cent,  phosphorus,  but  above  that  the  iron  is  liable 
to  be  weak  and  '  cold-short/  especially  under  impact.  In  fact, 
where  very  strong  iron  is  desired,  the  phosphorus  should  be  kept 
down  to  0.4  per  cent,  at  least. 

With  the  various  amounts  of  impurities  mentioned  above 
the  combined  carbon  will  be  in  the  neighborhood  of  1  per  cent, 
and  the  graphite  about  2.5  per  cent.,  the  exact  amounts  depending 
upon  the  thickness  of  the  castings  and  the  rate  at  which  they  are 
cooled.  If  we  desire  to  keep  the  combined  carbon  the  same  and 
reduce  the  graphite  it  will  be  necessary  to  reduce  the  total  carbon. 
This  can  be  accomplished  by  mixing  in  steel  scrap  and  melting 
fast  in  the  cupola,  or  by  melting  in  an  air-furnace  instead  of  a 
cupola.  This  reduction  in  graphite  results  in  a  closing  of  the 
grain  of  the  steel,  with  consequent  increase  in  strength  and 
density. 

Segregation.  —  A  common  cause  of  porosity  in  castings  is 
segregation,  or  the  collection  together  of  impurities  in  spots. 
This  segregation  is  the  greater  the  greater  the  amounts  of  phos- 


THE  CONSTITUTION   OF  CAST   IRON  349 

phorus,  sulphur,  manganese,  and  silicon.  Phosphorus  increases 
the  segregation  by  making  a  fluid  eutectic,  which  does  not  so- 
lidify until  after  the  remainder  of  the  casting,  but  then  runs 
into  that  part  of  the  metal  having  the  loosest  texture.  This 
part  is  usually  in  the  middle  of  the  larger  sections  of  the  cast- 
ing, and  when  the  silicon  is  high  and  there  are  shrinkage  spots  the 
segregation  will  be  excessive  in  the  neighborhood  of  these  spots. 
Manganese  and  sulphur  are  also  liable  to  collect  in  the  same  way 
and  place.  These  localities,  where  the  segregation  is  high,  and 
which  are  known,  when  very  bad,  as  'hot  spots/  are  sometimes 
porous  or  surrounded  by  porous  parts  of  the  casting.  They  are 
sometimes  so  extremely  hard  that  no  tool  will  cut  them.  One 
way  of  getting  rid  of  them  is  to  use  very  large  risers,  or  headers, 
which  solidify  last  and  serve  as  feeders  for  the  remainder  of  the 
metal.  Under  these  circumstances  the  segregation  occurs  in  the 
riser,  and  is  thus  temporarily  removed.  This  method  is  not  ad- 
visable as  a  regular  practice,  however,  because  these  risers  ulti- 
mately find  their  way  back  into  the  cupola  as  scrap  and  result  in 
increasing  the  impurities  in  a  subsequent  set  of  castings. 

Headers  themselves  increase  the  density  of  iron  castings  by 
feeding  the  metal  and  so  preventing  the  porous  spots,  and  also  by 
keeping  the  metal  under  a  pressure  during  solidification.  This 
latter  is  especially  serviceable  when  the  phosphorus  is  high,  which 
tends  to  make  the  metal  expand  during  solidification,  as  I  have 
shown. 

Checking.  —  The  time  when  a  casting  usually  checks  is  when 
it  is  just  above  the  black  heat,  when  the  metal  is  in  a  weak  and 
tender  condition  and,  as  shown  by  Fig.  257,  page  339,  is  under 
strain  because  it  is  contracting  upon  the  sand.  Sulphur  greatly 
increases  weakness  at  this  temperature,  because  both  sulphide 
of  manganese  and  sulphide  of  iron  are  now  in  a  pasty  condition, 
and  therefore  offer  very  little  resistance  to  breaking.  The  sulphide 
of  iron  is  much  worse,  however,  because  this  is  spread  out  in  thin 
plates  or  membranes  which  offer  much  more  extended  planes  of 
weakness  than  the  sulphide  of  manganese,  which  is  in  small  spots 
or  bubbles,  resembling  blow-holes  in  its  effect.  Phosphorus,  by 
decreasing  shrinkage,  decreases  the  liability  of  checking,  but  phos- 
phorus ha-s  another  influence,  shown  in  the  production  of  large- 
sized  crystals,  and  in  this  respect  it  increases  the  liability  of  the 
metal  to  check. 


350  THE  METALLURGY  OF   IRON  AND   STEEL 

Manganese,  by  decreasing  the  size  of  crystals,  tends  to  counter- 
act partially  the  effect  of  the  phosphorus.  The  size  of  crystals 
can  also  be  decreased  to  some  extent  by  chilling  the  weak 
points  and  feeding  them  well  under  a  head  of  metal.  Feeding  all 
localities  liable  to  check  has  the  double  advantage  of  lessening 
shrinkage  and  segregation,  both  of  which  increase  the  liability  to 
checking. 

Softness,  Workability,  and  Strength.  —  It  is  the  combined  car- 
bon which  is  the  great  hardener  of  cast  iron,  the  other  elements 
producing  hardness  chiefly  in  proportion  as  they  produce  com- 
bined carbon,  except  manganese,  which  not  only  produces  com- 
bined carbon,  but  also  produces  a  compound  having  the  formula 
(FeMn)3C,  which  is  very  hard  and  difficult  to  machine. 

Silicon,  by  decreasing  combined  carbon,  decreases  hardness. 
When  we  get  above  3  per  cent,  silicon,  however,  there  begin  to 
form  new  compounds  with  silicon  which  make  the  iron  hard. 
Furthermore,  silicon  above  3  per  cent,  increases  combined  carbon, 
instead  of  decreasing  it. 

The  maximum  softness  of  cast  iron  is  obtained  with  about 
2.5  to  3  per  cent,  of  silicon,  the  sulphur  being  not  above  0.1  per 
cent,  and  the  manganese  not  above  0.4  per  cent.  In  large  or 
slowly  cooled  castings  the  silicon  should  be  near  the  lower  limit, 
and  in  small  or  rapidly  cooled  castings  near  the  upper  limit,  in 
order  that  the  combined  carbon  may  be  down  below  0.15  per 
cent,  and  the  graphite  more  than  3  per  cent.  Such  a  cast  iron 
would  correspond  to  a  soft  steel,  mechanically  mixed  with  crystals 
of  graphite.  This  soft  steel  would  machine  with  great  ease,  and 
the  graphite  would  act  as  a  lubricant  for  the  cutting  tool.  The 
mixture  will  have  a  transverse  strength  of  about  2000  to  2200 
lb.,  will  be  low  in  density  and  open  in  grain.  To  increase  the 
strength  without  increasing  the  hardness,  the  best  way  is  to  cut 
the  sulphur  and  phosphorus  down  to  a  low  point,  if  possible, 
because  sulphur,  and  next  to  it  phosphorus,  are  the  impurities 
which  weaken  iron  most  (aside  from  their  influence  on  carbon). 
Another  way  is  to  decrease  the  total  carbon,  and  hence  the  graphite, 
because  graphite  crystals,  especially  if  large,  are  great  weakeners 
of  cast  iron. 

The  strength  of  steel  is  more  than  double  the  strength  of 
cast  iron,  the  difference  being  due  almost  altogether  to  the  graphite 
in  cast  iron,  because  silicon  in  itself  (aside  from  its  influence  on 


THE  CONSTITUTION  OF  CAST   IRON  351 

the  carbon)  is  a  strengthener  of  both  iron  and  steel  up  to  at  least 
4  per  cent. 

To  a  slight  extent  the  total  carbon  may  be  reduced  by  melting 
steel  scrap  with  the  iron,  or  by  decreasing  the  amount  of  man- 
ganese, provided  that  the  manganese  left  be  always  at  least  twice 
the  sulphur,  otherwise  the  iron  will  be  weak  and  brittle. 

The  strength  of  cast  iron  may  be  increased  by  increasing 
the  combined  carbon,  but  this  is  done  at  the  expense  of  softness 
and  workability.  Cast  iron  containing  from  1.5  to  2  per  cent, 
of  silicon  (depending  upon  the  size  of  the  castings  and  rate  of 
cooling),  0.9  per  cent,  of  combined  carbon,  0.5  per  cent,  of 
manganese  and  not  more  than  0.08  per  cent,  of  sulphur  and  0.3 
per  cent,  of  phosphorus,  will  work  without  difficulty  in  the  machine 
shop  and  have  a  tensile  strength  of  over  28,000  Ib.  per  square 
inch.  In  many  cases  foundries  are  unwilling  to  go  to  the  expense 
of  such  a  low  sulphur  and  phosphorus.  In  this  case  the  strength 
must  be  obtained  by  raising  the  manganese,  which  is  not  advisable, 
as  it  decreases  the  softness  more  than  any  other  element,  causes 
dull  iron  and  high  total  carbon. 

An  important  point  in  connection  with  the  strength  of  cast 
iron  is  the  size  of  the  crystals  of  graphite — the  smaller  these 
crystals  are  the  greater  the  strength,  because  the  smaller  are  the 
planes  of  easy  rupture.  A  notable  example  of  this  is  malleable 
cast  iron,  which  may  have  a  tensile  strength  of  45,000  Ib.  per 
square  inch,  even  when  the  percentage  of  graphitic  or  temper 
carbon  is  as  high  as  3  per  cent.  The  very  small  size  of  the  flakes 
of  the  temper  carbon  does  not  reduce  the  strength  as  much  as  the 
same  amount  of  the  larger  graphite  crystals. 

It  is  believed  by  many  that  smaller  graphite  crystals  are 
obtained  by  mixing  different  brands  of  iron  in  the  cupola,  even 
though  the  analysis  of  the  mixture  may  be  the  same.  This, 
however,  is  denied  by  others,  and  no  reliable  data  exist  upon 
which  we  can  base  a  definite  statement.  It  is  also  believed  by 
many  that  when  the  silicon  is  added  to  the  cast  iron  immediately 
before  pouring  into  the  molds,  the  crystals  of  graphite  are  smaller 
than  those  formed  when  high-silicon  irons  are  melted  in  the  cupola. 
The  practice  of  adding  a  small  amount  of  ferrosilicon  to  the  ladle 
of  cast  iron  after  it  is  received  from  the  cupola  is  thus  said  to  be 
doubly  advantageous,  because  the  silicon  does  not  have  to  go 
through  the  cupola,  where  it  suffers  some  oxidation,  and  it  pro- 


352 


THE  METALLURGY  OF   IRON  AND   STEEL 


duces  the  desired  softness  by  precipitating  the  graphite,  but  in  a 
form  which  does  not  decrease  strength  so  much. 

To  obtain  high  transverse  strength,  the  silicon  should  be 
about  0.2  per  cent,  lower  and  the  combined  carbon  about  0.2 
per  cent,  higher  than  the  figures  given  for  tensile  strength.  Other- 
wise the  effects  are  very  similar. 

Some  estimates  of  the  strength  and  workability  of  cast  iron 
are  given  in  the  following  table,1  and  on  page  57  of  No.  94. 

TABLE  OF  CAST-IRON  STRENGTH  AND  WORKABILITY 


Silicon 
Per 
Cent. 

Sulphur 
Per 
Cent. 

Phos- 
phorus 
Per 
Cent. 

Man- 
ganese 
Per 
Cent. 

Tensile 
Strength 
Ib 

Trans- 
verse 
Strength 
Ib 

Soft  iron  for  pulleys,  small  j 
castings,  good  tooling  j 

2.20 
to 
2.80 

Not 
over 
0.085 

Not 
over 
0.70 

0.30 

to 
0.70 

28,000 

2200 

Medium   iron   for   engine  j 
cylinders,  gears,  etc  .  .  j 

1.40 
to 
2.00 

Not 
over 
0.085 

Not 
over 
0.70 

0.30 
to 
0.70 

30,000 

2500 

Hard-iron    cylinders    for  ( 

1.20 

ammonia,       air-corn-  -j 

to' 

pressors,  etc  ( 

•1.60 
1.60J 

Not 
over 

0.70 
to 

Not 

over 

25,000 

2800 

tQ2 

0.095 

0.40 

0.60 

1.90 

If  annealed. 


2  If  cooled  fast. 


Chill.  —  In  the  making  of  cast-iron  rolls,  railroad  car  wheels, 
anvils,  etc.,  at  least  one  surface  of  the  casting  is  desired  to  have 
great  hardness,  to  resist  wear,  and  to  be  backed  by  metal  which 
shall  be  stronger  and  not  so  brittle.  This  is  accomplished  by 
chilling  the  surface  that  is  wanted  in  a  hard  condition,  and  so 
producing  white  cast  iron  to  varying  depths,  regulated  at  the 
will  of  the  foundrymen.  The  making  of  this  kind  of  casting  is 
one  of  the  most  difficult  problems  of  cast-iron  metallurgy.  The 
metal  must  be  very  close  to  the  given  composition,  and  the 
temperature  of  the  mold,  of  the  chill,  and  of  the  metal  when 
cast  must  be  regulated  with  care.  Therefore,  air-furnaces  are 
often  employed  for  melting  in  this  class  of  work,  or  else  uniform 

1  Abstracted  from  page  197  of  No.  120,  page  355. 

•§ 


FIG.    258. —WHITE    PIG    IRON. 

0.75  per  cent.  Si.     0.120  per  cent.  S.      50 

diameters.     Unetched. 


FIG.    259. —  GRAY   PIG   IRON. 

0.75   per   cent.    Si.     0.012   per   cent.    S. 

50  diameters.     Unetched. 


FIG.    260. —GRAY   PIG    IRON. 

1.75   per   cent.    Si.     0.025    per   cent.    S. 

50  diameters.     Unetched. 


FIG.    261. —  GRAY   PIG   IRON. 

2.5  per  cent.  Si.     0.012  per  cent.  S.     50 

diameters.     Unetched. 


FIG.    262. —  GRAY   PIG   IRON. 

3.5  per  cent.  Si.     0.025  per  cent.  S.     50 

diameters.     Unetched. 


FIG.  263.  — NO.  2  CHARCOAL  PIG  IRON 

VERY  SLOWLY  COOLED. 

50  diameters.     HNO3. 


354 


THE   METALLURGY   OF   IRON   AND   STEEL 


conditions  of  cupola  melting  are  maintained  with  great  care,  and 
very  little,  if  any,  scrap,  which  must  necessarily  be  of  somewhat 
uncertain  analysis,  is  used,  except  the  return  scrap  from  the 
foundry  itself,  that  is,  defective  castings,  sprues,  gates,  shot-iron 
spillings,  etc.,  and  also  scrap  castings  of  like  nature,  such  as 
worn-out  car  wheels  and  broken  rolls.  The  most  important 


FI6.  264.  —  METHOD  OF  MEASURING  THE  DEPTH  OF  CLEAR  CHILL  IN  A 
CAST-IRON   ROLL. 

factors  in  regulating  the  depth  of  the  chill  are  the  silicon  and  the 
sulphur,  and  in  the  following  table  is  given  the  depth  of  clear 
chill  from  the  surface  for  several  different  percentages  of  silicon 
and  sulphur.  The  figures  here  given  must  only  be  taken  as  ap- 
proximations, as  they  will  vary  to  an  important  extent  with 
different  conditions  in  each  foundry;  but,  starting  with  this  as  a 
basis,  one  can  quickly  prepare  a  table  for  himself  to  suit  the 
practice  in  his  foundry.  Phosphorus  has  very  little  effect  on  the 
depth  of  chill,  and  manganese  is  also  relatively  less  effective, 
although  it  increases  the  hardness  of  the  chilled  portion.  The 
hotter  the  iron  when  cast  the  deeper  the  chill. 


THE   CONSTITUTION    OF   CAST   IRON 


355 


DEPTHS  OF  CLEAR  CHILL  FROM  SURFACE  IN  INCHES 


Silicon 
Per  Cent. 

Sulphur 
0.2 
Per  Cent. 

Sulphur 
0.15 
Per  Cent. 

Sulphur 
0.1 
Per  Cent. 

Sulphur 
0.075 
Per  Cent. 

Sulphur 
0.05 
Per  Cent. 

1    25 

0  625 

0  250 

0  125 

0  000 

0  000 

1.00  
0  75 

1.000 
1  500 

0.625 
1  000 

0.250 
0  625 

0.125 
0  250 

0.000 
0  125 

0.50 

1  500 

1  000 

0  625 

0  250 

0.40 

1  250 

1  000 

0  625 

0.30  

1.500 

1.000 

REFERENCES  ON  THE  CONSTITUTION  OF  CAST  IRON 

See  Nos.  1,  32,  90,  91,  93,  and 

120.  W.  G.  Scott.     "  Effect  of  Variations  in  the  Constituents  of 

Cast  Iron."  Proceedings  of  the  American  Society  for 
Testing  Materials,  vol.  ii,  1902,  pages  181-206. 

121.  Transactions  of  the  American  Foundrymen's  Association. 

122.  G.    B.    Upton.     "The     Iron-Carbon     Equilibrium."     The 

Journal  of  Physical  Chemistry,  October,  1908,  vol.  xii, 
pages  507-549.  This  is  a  very  valuable  study  and  resume 
of  the  recent  researches  on  the  constitution  of  all  the  alloys 
of  iron  and  carbon,  and  gives  the  chief  known  facts  of 
scientific  interest  in  a  concise  form. 


XIII 
MALLEABLE    CAST   IRON 

MALLEABLE  cast  iron  is  iron  which,  when  first  made,  is  cast  in 
the  condition  of  cast  iron,  and  is  made  malleable  by  subsequent 
treatment  without  fusion.  Gray  cast  iron  is  weak  and  brittle,  on 
account  of  the  flakes  of  graphite  which  destroy  its  continuity  and 
form  planes  of  easy  yielding.  It  will  readily  be  understood  that  if 
the  amount  of  graphite  were  less,  or  if  its  flakes  occurred  in  a  very 
finely  pulverized  form,  or  both,  the  material  would  be  stronger  and 
would  endure  a  slight  degree  of  deformation  without  cracking; 
that  is,  it  would  be  malleable.  These  changes  are  indeed  brought 
about  in  the  manufacture  of  malleable  cast  iron.  The  process, 
which  was  invented  by  Reaumur  in  1722,  but  has  only  been  in 
practical  use  about  100  years  and  of  importance  less  than  50,  is  a 
very  ingenious  operation.  Malleable  castings  have  two  of  the 
greatest  advantages  of  cast  iron;  namely,  fluidity  and  a  low  melt- 
ing-point, combined  with  about  three-quarters  the  strength  and 
one-sixth  the  ductility  of  steel.  They  are  very  popular  for  rail- 
road rolling-stock  construction,  especially  for  draw-bars,  couplers 
and  knuckles,  on  account  of  their  high  resiliency,  resistance  to 
shocks,  and  ability  to  be  made  into  thin,  light  castings.  Probably 
about  one-half  of  the  malleable  cast-iron  production  of  the  United 
States  goes  into  railroad  work,  although  it  is  to  be  observed  that  at 
present  the  use  of  steel  castings  for  this  purpose  is  increasing  rela- 
tively faster.  The  next  most  important  use  is  for  pipe-fittings, 
where  malleable  cast  iron  is  equally  advantageous;  also  for  small 
machinery  castings  needing  to  be  strong  and  light,  household  and 
building  hardware,  etc. 

Process.  —  Pig  iron  of  the  proper  kind  is  first  melted  and  cast 
into  molds  of  the  desired  size  and  shape.  In  these  operations  two 
precautions  are  observed:  first,  the  proportion  of  silicon  is  low, 
and  second,  the  castings  are  not  allowed  to  cool  too  slowly.  We 
have  already  learned  that  the  precipitation  of  graphite  is  a  slow 

356 


MALLEABLE  CAST   IRON 


357 


action  and  does  not  occur  unless  ample  time  is  allowed  or  there  is 
sufficient  silicon  to  produce  a  strong  chemical  action.  In  the  in- 
tentional absence  of  these  factors  malleable  castings,  as  first  made, 
are  practically  free  from  graphite  and  consist  entirely  of  white  cast 
iron  —  hard,  brittle  and  weak. 

After  cooling  the  castings  are  cleaned  and  packed  in  some  pul- 
verized material,  as  iron  ore,  mill  scale,  lime,  sand,  placed  in  an 
annealing  furnace  and  heated  to  a  temperature  of  675°  to  725°  C. 
(1250°  to  1350°  F.),  which  is,  roughly,  450°  C.  below  their  melting- 
point,  and  at  which  temperature  they  are  kept  for  many  hours. 
While  under  this  heat  there  oc- 
curs the  precipitation  of  graph- 
ite, which  normally  should  have 
occurred  during  solidification,  or 
shortly  thereafter,  and  in  the 
majority  of  cases  almost  all  the 
combined  carbon  throughout  the 
body  of  the  casting  is  changed 
to  graphite.  But  the  graphite 
does  not  here  form  in  flakes,  as 
in  ordinary  gray  cast  iron,  but  in 
a  finely  comminuted  condition, 
like  a  powder,  to  which  the 
name  of  '  temper  carbon '  or 
'temper  graphite'  is  given  (see 
Fig.  265) .  In  this  form  it  is  not 

nearly  so  weakening  or  embrittling  to  the  casting  as  flakes  of 
graphite  would  be.1 

Properties  of  Malleable  Cast  Iron.  —  Malleable  cast  iron  con- 
sists almost  entirely  of  ferrite  and  temper  carbon.  It  has  a  tensile 
strength  of  40,000  to  60,000  pounds  per  square  inch,  which  is  about 
double  that  of  gray  cast  iron,  with  an  elongation  of  2£  to  5J  per 
cent,  in  2  in.  and  a  reduction  of  area  of  2  J  to  8  per  cent.2  A  one- 
inch  square  bar  on  supports  12  inches  apart  should  bear  a  load  at 

1  We  may  liken  this  to  two  samples  of  putty,  in  one  of  which  had  been 
embedded  a  large  number  of  plates  of  mica,  and  in  the  other  the  same  amount 
of  mica  ground  to  powder. 

2  In  the  case  of  iron  very  carefully  melted  and  annealed  in  iron  oxide,  the 
elongation  may  go  as  high  as  8  per  cent,  and  the  reduction  of  area  as  high  as 
12  per  cent. 


FIG.    265.  —  ANNEALED    MALLE- 
ABLE  CAST   IRON. 

Magnified  50  diameters.     Unetched. 


358 


THE  METALLURGY  OF   IRON  AND   STEEL 


the  center  of  at  least  3500  pounds,  and  be  deflected  at  least  half  an 
inch  before  breaking.  Thin  sections  should  be  capable  of  flatten- 
ing out  under  a  hammer  and  bending  double  without  cracking. 

Total  Carbon  in  Malleable  Cast  Iron.  —  In  melting  the  iron  we 
take  pains  to  produce  a  low  total  carbon,  and  if  we  anneal  in  iron 
ore  or  mill  scale  the  carbon  is  still  further  reduced  by  a  curious 
reaction  which  takes  place  between  it  and  the  iron  oxide  — 
3  C  +  Fe3  O3  =  3  CO  +  2  Fe, 

whereby  it  forms  carbon  monoxide  and  is  eliminated.  Sometimes, 
when  the  sections  of  metal  are  thin,  we  may  eliminate  almost  all 
the  carbon  to  the  very  center  of  the  casting,  which  makes  a  more 
ductile  material.  It  must  be  observed,  however,  that  this  reduc- 
tion of  carbon  is  not  an  essential  feature  of  annealing  and  that  the 
real  function  of  this  operation  is  to  change  the  combined  carbon  to 
temper  carbon,  for  the  malleable  cast  iron  owes  its  superiority  over 


FIG.   266.  —  AIR-FURNACE. 


gray  cast  iron  chiefly  to  the  finely  pulverized  form  of  its  temper 
carbon. 

Melting  in  the  Air-Furnace.  —  The  commonest  melting-furnace 
for  malleable  cast  iron  is  the  air-furnace,  because  thereby  we  get  a 
better  control  of  the  metal  than  in  the  cupola  and  the  ability  to 
produce  castings  with  lower  total  carbon,  lower  sulphur,  and  any 
desired  amount  of  silicon.  After  the  metal  is  melted  it  is  retained 
in  this  furnace  for  15  minutes  to  an  hour  longer,  and  test  samples 
are  taken  at  intervals,  from  the  fracture  of  which  and  the  tem- 
perature of  the  iron  we  determine  the  correct  moment  for  tapping. 
The  fracture  of  the  test  ingot  sample  should  be  a  clear  white 
throughout,  except  when  the  castings  are  to  be  of  very  light  sec- 
tion, in  which  case  the  metal  might  be  tapped  when  the  test  sample 


MALLEABLE   CAST  IRON 


359 


shows  a  few  specks  of  graphite  in  the  center.  The  practice  of 
judging  from  test  samples  is  different  in  each  foundry,  but  there 
must  be  some  system  which  insures  that  the  metal  shall  be  of  such 


Modified 

Pittsbucg  Type  Air  Furnace 
Cap.  1 5  Tons 


a  composition  when  tapped  that  the  castings  will  have  not  more 
than  a  trace  of  graphite  if  any  at  all  (say,  less  than  0.15  per  cent, 
in  small  castings  and  a  little  more  in  larger  ones).  It  is  to  be 
remembered  that  any  graphite  is  a  detriment.  The  longer  in  the 


360 


THE  METALLURGY  OF   IRON  AND  STEEL 


furnace  after  melting  the  more  silicon  will  be  burned  out,  and 
therefore  the  less  the  liability  to  graphite.  Consequently,  the 
hotter  we  want  to  get  the  iron  the  higher  must  be  the  percentage  of 
silicon  in  it  to  start  with.  Also,  the  longer  the  metal  is  in  the  fur- 
nace after  melting  the  more  carbon  will  be  burned  out  of  it.  (See 
also  pp.  284-286.)  During  the  operation  the  bath  is  rabbled  at 
intervals,  and  is  skimmed  so  as  to  expose  the  metal  directly  to 
oxidation  by  the  gases. 

Tapping  the  Air-Furnace.  —  When  the  time  comes  to  tap  the 
furnace  we  may  either  allow  a  small  stream  to  flow,  which  is  caught 


FIG.    268. 

in  ladles  and  immediately  poured  into  the  castings,  whereby  it 
takes  from  20  minutes  to  an  hour  to  empty  a  furnace  of  10  to  30 
tons  capacity,  or  else  we  may  allow  the  metal  to  run  out  in  a  big 
stream  into  a  large  ladle,  from  which  it  is  repoured  into  smaller 
ones  for  casting.  The  first  method  gives  a  less  uniform  product, 
because  the  last  part  of  the  bath  having  been  exposed  longer  to 
the  oxidizing  influence  of  the  furnace,  is  lower  in  silicon  and  total 
carbon  than  the  first  part.  This  is  not  altogether  a  disadvantage, 
however,  because  the  first  metal,  having  come  from  the  top  of  the 


MALLEABLE  CAST   IRON 


361 


bath  nearer  the  flame,  is  hotter,  and  therefore  very  suitable  to  pour 
into  smaller  castings;  and  these  smaller  castings,  because  they  cool 
more  rapidly,  can  well  contain  more  silicon  without  danger  of 
graphite  precipitating.  Moreover,  the  hotter  the  metal  the  greater 
the  tendency  for  it  to  be  white.  A  disadvantage  of  pouring  the 
metal  first  into  a  big  ladle  is  that  it  must  be  hotter  when  it  comes 
from  the  furnace,  and  moreover  the  first  ladle  must  be  preheated. 
A  middle  course  is  possible :  we  may  pour  the  top  of  the  bath  into 
small  castings  by  means  of  ladles  receiving  their  metal  direct  from 
the  furnace  tap-hole,  and  then  enlarge  the  tap-hole  and  take  all  the 


FIG.    269. 


rest  of  the  bath  into  a  big  ladle,  whence  it  can  be  poured  into  other 
ladles  and  go  to  the  larger-sized  castings. 

Cupola  Melting.  —  In  cupola  melting  we  get  metal  having 
practically  the  same  composition  at  all  times  of  the  heat,1  and  also 
about  the  same  temperature.  It  is  also  cheaper  in  fuel,  and 
especially  so  when  it  is  desired  to  get  very  fluid  iron,  because  ob- 
taining hot  iron  in  the  air-furnace  requires  a  continuation  of  the 
heating  after  the  iron  is  melted,  and  this  entails  not  only  the  use  of 
more  fuel,  but  also  a  burning  out  of  silicon  and  carbon,  both  of 
which  elements  increase  the  fluidity  of  the  metal.2  Cupola  metal 
is  higher  in  total  carbon  and  in  sulphur,  both  of  which  decrease 

1  Except  for  the  slightly  higher  sulphur  at  the  beginning  and  end. 

2  When  I  say  'hot  iron'  here,  I  mean  'fluid  iron/  i.  e.,  the  degree  of  heat 
above  the  melting-point ;  and  in  this  sense  hotness  includes  both  the  tempera- 
ture and  the  state  of  impurity.     An  iron  with  2  per  cent,  total  carbon  and 
0.60  per  cent,  silicon  at  1300°  C.  (2375°  F.)  will  not  be  nearly  as  fluid  or  as 
far  above  its  melting-point  as  one  with  3  per  cent,  total  carbon  and  0.75  per 
cent,  silicon  at  the  same  temperature. 


362 


THE  METALLURGY  OF  IRON  AND   STEEL 


strength  and  ductility.  Because  of  the  higher  total  carbon  it  is 
more  difficult  to  prevent  graphite  separating;  therefore  cupola 
metal  is  used  for  light  castings,  which  cool  more  quickly  and  do 
not  usually  require  so  much  strength. 

Regenerative  open-hearth  furnaces  are  also  used  in  melting 
iron  for  malleable  castings.  (See  also  pages  285-286.) 

Annealing-Boxes.  —  After  the  castings  are  cooled  they  are 
carefully  cleaned  from  all  adhering  sand  by  tumbling  them  around 
in  a  tumbling-barrel  (in  which  they  are  mixed  with  star-shaped 


FIG.    270.  —  TUMBLING-BARREL. 

pieces  of  metal  something  like  children's  jackstones),  or  by  sand- 
blast, or  by  some  other  suitable  method.  They  are  then  packed  in 
the  cast-iron  '  saggers '  or  annealing  pots,  or  boxes,  together  with 
the  packing.  Sometimes,  though  rarely,  the  tops  of  the  saggers 
are  closed  by  means  of  an  iron  cover,  sometimes  by  a  thick  layer 
of  the  packing  in  the  upper  part,  and  sometimes  by  clay  or  wheel- 
swarf.  These  pots  last  only  from  4  to  20  heats  before  they  are 
largely  oxidized  away. 


MALLEABLE  CAST  IRON 


363 


Annealing-Ovens.  — The  boxes  are  then  placed  in  the  anneal- 
ing-ovens in  such  a  way  that  the  flame  may  play  around  them  as 
completely  as  possible.  The  general  form  of  ovens  is  shown  in 


— v 

n 


»4 

IJi 


-H 


t 


•> 


jK 

I  o 


Figs.  271  and  273.  The  flame  usually  comes  in  at  the  top  and  goes 
out  at  the  bottom  along  the  side,  and  thence  through  flues  under- 
neath the  oven.  The  fuel  used  may  be  coke,  coal,  oil  or  gas,  the 


364  THE  METALLURGY  OF   IRON  AND   STEEL 

latter  being  preferable  on  account  of  the  better  control  of  the  tem- 
perature, which  should  be  increased  at  a  very  gradual  and  uniform 
rate  during  the  heating  up,  and  kept  as  constant  as  possible  during 
the  annealing  period. 

Annealing  Practice.  —  It  takes  about  six  days  for  the1  anneal- 
ing operation,  including  heating  up  and  cooling  down.  Sometimes 
this  can  be  shortened  a  little  by  decreasing  the  time  at  the  full 
annealing  heat,  and  by  cooling  rapidly  or  drawing  the  saggers  out 
of  the  oven  and  dumping  them  while  the  contents  are  still  at  a 
dull-red  heat.  This  practice  is  not  conducive  to  a  good  quality  of 
castings  and  should  never  be  permitted  in  important  cases.  The 
time  at  the  full  heat  should  never  be  less  than  60  hours,  and  pref- 
erably it  should  be  more  than  that.  If  less,  the  temperature  of 
annealing  must  be  higher,  and  this  decreases  the  strength  and 
ductility  of  the  castings.  Annealing  should  not  occupy  too  long  a 
time,  however,  unless  the  temperature  is  quite  low,  ^because  the 
temper  carbon  tends  to  draw  together  to  larger  flakes;  besides 
which  the  metal  may  become  oxidized  between  the  grains,  or 
"burnt.'  Air-furnace  castings  should  be  annealed  at  675°  to  760°  C. 
(1250°  to  1400°  F.)  and  cupola  metal  at  850°  to  950°  C.  (1560°  to 
1750°  F.). 

Packing.  —  As  originally  planned,  the  castings  were  annealed 
in  a  packing  of  iron  oxide  crushed  to  a  size  less  than  a  quarter  of 
an  inch  in  diameter.  The  packing  must  surround  the  castings  at 
every  place,  both  inside  and  out,  and  no  two  castings  must  touch. 
Iron  ore,  mill  scale,  'bull-dog/  and  similar  forms  of  iron 
oxide  are  used  for  this  purpose.  Usually  two  or  three  parts  of  old 
packing  are  used  with  one  part  of  new  packing,  because  all  new 
packing  is  too  energetic  in  its  chemical  action  on  the  carbon,  and 
all  old  packing  will  not  be  energetic  enough  in  decarburizing  the 
surface  of  the  castings. 

Annealing  in  iron  oxide  produces  a  white  skin  where  the  casting 
has  been  deprived  of  its  carbon,  and  a  black  interior,  due  to  the 
temper  carbon;  whence  the  name  of  ' black  heart  malleable'  for 
this  material.  Tests  have  shown  that  the  casting  with  this  white 
skin  upon  it  is  much  stronger  than  a  similar  one  which  has  not  been 
decarburized  on  the  surface,  and  therefore  the  packing  in  iron 
oxide  is  advantageous,  even  though  not  an  essential  feature  of  the 
operation.  When  the  castings  are  packed  in  some  nonoxidizing 
material,  such  as  sand,  clay  or  lime,  they  may  receive  as  perfect 


MALLEABLE  CAST   IRON  365 

an  annealing,  as  far  as  the  production  of  temper  carbon  is  con- 
cerned, but  will  be  without  the  white  skin  and  of  lower  strength. 

Composition  of  Iron  Used.  —  The  pig  iron  employed  in  this 
process  is  sold  under  the  name  of  '  malleable  coke  iron'  or  '  malle- 
able Bessemer/  As  it  is  the  composition  of  the  metal  poured 
into  the  molds  which  determines  the  success  of  the  annealing  and 
the  quality  of  the  product,  we  shall  consider  first  the  kind  of 
metal  needed  there,  and  from  that  calculate  the  composition 
of  the  mixture  necessary  to  charge  into  the  air-furnace  or  cupola. 
In  the  air-furnace  we  do  not  judge  the  iron  by  its  chemical  analysis, 
but  by  the  appearance  of  the  test-ingot  fracture  when  we  are 
ready  to  pour,  but  as  the  second  quality  depends  upon  the  first, 
it  is  the  same  thing  in  the  end. 

Silicon.  —  The  proportion  of  silicon  will  depend  upon  the  size 
of  the  casting  and  the  amount  of  total  carbon,  because  the  greater 
each  of  these  is  the  less  will  be  the  amount  of  silicon  that  will  cause 
a  precipitation.  It  might  at  first  appear  that  the  less  silicon  the 
better;  but  this  is  not  altogether  so,  because  temper  carbon  will 
not  come  out  during  annealing  unless  a  certain  amount  of  silicon  is 
present ;  and  the  more  there  is,  the  more  quickly,  easily,  and  com- 
pletely will  the  precipitation  occur.  For  castings  one  inch  thick 
the  silicon  may  be  as  low  as  0.35  per  cent.;  but  this  is  unusual,  as 
three-quarters  of  an  inch  thickness  is  rarely  exceeded.  For  half- 
inch  castings  the  silicon  will  be  about  0.60  per  cent.,  and  for  very 
thin  and  light  castings  with  low  total  carbon  and  high  sulphur 
(say  0.2  to  0.3  per  cent.),  the  silicon  may  be  up  to  1  per  cent.  To 
the  percentage  of  silicon  desired  in  the  castings  we  must  add  the 
amount  which  will  he  burned  out  in  melting.  In  the  cupola  this 
will  be  about  0.2  to  0.25  per  cent.,  and  in  the  air-furnace  from 
0.15  to  0.5  per  cent.,  or  more  if  desired,  depending  on  the  length  of 
time  the  metal  is  kept  in  the  furnace  after  melting.  The  hotter 
we  want  the  iron  or  the  more  total  carbon  we  desire  to  burn  out, 
the  longer  this  time  must  be,  and  therefore  the  higher  the  silicon 
in  the  original  mixture  charged. 

Sulphur.  —  Sulphur  increases  the  tendency  of  castings  to 
check,  which  is  especially  important  in  malleable  work  on  account 
of  the  shrinkage  of  white  iron  being  nearly  double  that  of  gray 
iron.  Sulphur  also  reduces  the  strength  and  the  ease  of  annealing. 
For  this  reason  over  0.06  per  cent,  should  not  be  permitted  in  cast- 
ings requiring  strength,  but  it  actually  runs  up  to  0.2  and  0.3  per 


366  THE  METALLURGY  OF   IRON  AND   STEEL 

cent,  in  inferior  metal,  both  in  America  and  England,  and  espe- 
cially in  small  castings,  which  do  not  need  strength  so  much,  and 
which,  having  less  length  for  shrinkage,  are  not  so  liable  to  be 
checked  by  cooling  strains. 

Manganese.  —  Low  manganese  is  preferred  by  many  foundries, 
and  one  of  the  highest  authorities  in  America  1  places  the  limit  at 
0.8  per  cent.  It  should  be  remembered,  however,  that  the  man- 
ganese should  be  at  least  twice  the  sulphur,  and  preferably  three 
times,  though  not  when  the  sulphur  is  as  high  as  0.3  per  cent. 
Manganese  of  0.5  per  cent,  tends  to  decrease  checking.  It  also 
protects  silicon  from  oxidation,  both  during  melting  and  anneal- 
ing, and  on  this  account  hastens  and  makes  more  complete  the 
precipitation  of  temper  carbon.  It  also  protects  the  iron  itself 
from  oxidation  during  annealing  and  thus  prevents  the  formation 
of  'scaled7  castings.  More  than  0.6  per  cent,  manganese  makes 
the  iron  hard  and  difficult  to  machine,  which  is  disadvantageous, 
especially  for  pipe-fittings,  which  must  be  threaded  with  great 
economy  in  order  to  meet  the  trade  competition. 

Phosphorus.  —  Phosphorus  makes  the  metal  fluid,  which  is 
especially  desirable  where  total  carbon  and  silicon  are  low,  or 
where  sulphur  and  manganese  are  high.  On  the  other  hand,  it 
diminishes  two  of  the  most  valuable  properties  of  the  material: 
its  resiliency  and  resistance  to  shocks.  It  also  makes  the  metal 
hard,  difficult  to  machine  and  liable  to  check,  and  amounts  over 
0.225  per  cent,  should  never  be  permitted  by  engineers  where  the 
castings  are  subjected  to  strain. 

Total  Carbon.  —  Total  carbon  below  2.75  per  cent,  gives 
trouble  in  annealing  and  therefore  makes  the  castings  weak.  It 
also  makes  the  metal  more  sluggish.  It  is  difficult  to  get  as  low 
as  this  in  cupola  melting,  although  mixing  in  large  percentages  of 
steel  scrap  and  allowing  the  metal  to  run  out  of  the  cupola  as  fast 
as  melted  will  reduce  the  proportion  appreciably.  In  air-furnace 
practice  the  total  carbon  may  be  reduced  as  far  as  necessary. 
Annealing  in  iron  oxides  also  removes  carbon  from  the  outer  layers 
and  even  to  the  very  center  of  thin  castings.  The  lower  the  total 
carbon  in  the  annealed  castings,  the  better. 

Scrap  Used.  —  Not  more  than  about  20  per  cent,  of  bought 
scrap  is  used  on  the  average  in  American  practice,  and  a  good  deal 
of  this  is  steel,  on  account  of  the  desirability  of  lower  total  carbon, 
1  See  No.  130,  page  369. 


MALLEABLE  CAST   IRON 


367 


and  because  iron  scrap  is  too  impure,  too  variable  and  too  uncer- 
tain in  sampling  and  chemical  analysis  for  castings  requiring 
strength,  such  as  those  for  railroads  and  machinery.  There  is, 
however,  always  a  large  amount  of  '  return  scrap '  from  the  foun- 
dry, consisting  of  defective  castings,  sprues,  gates,  etc.,  which,  in 
the  case  of  small  castings,  may  be  greater  in  weight  than  the  cast- 
ings themselves.  This  return  scrap  is  low  in  total  carbon  and 
silicon  as  a  result  of  having  already  suffered  the  melting  changes. 

Shrinkage.  —  The  shrinkage  of  malleable  iron  from  casting  is 
almost  as  great  as  that  of  steel,  because  almost  no  graphite  forms. 
The  amount  of  silicon  and  the  sectional  area  of  the  castings  are 
still  the  determining  factors  in  this  connection.  Indeed,  by  means 
of  the  measurement  of  the  section  and  the  percentage  of  silicon  we 
may  estimate  the  shrinkage,  or  by  means  of  the  section  and  the 
shrinkage  we  may  estimate  the  silicon  very  closely,  other  condi- 
tions and  impurities  being  normal.  The  following  table  gives  the 
necessary  data  for  these  estimations : 


SHRINKAGE  IN  INCHES  PER  FOOT  OF  LENGTH 


PERCENTAGE 
OP  SILICON 

1  Inch 
Square 

i  Inch 
Square 

f  Inch 
Square 

1  Inch 
Square 

0  35 

0  225 

0  200 

0.190 

0   175 

0  50 

0  220 

0  195 

0  183 

0  170 

0  75 

0  215 

0  190 

0.176 

0.162 

1  00 

0  211 

0  183 

0.137 

0.102 

Expansion  due  to  Temper  Carbon.  —  It  is  a  very  interesting  fact 
that  when  the  malleable  cast  iron  is  annealed  and  the  temper 
carbon  precipitates,  the  casting  expands  to  an  amount  approxi- 
mately equal  to  that  which  would  have  occurred  if  the  graphite  had 
separated  during  solidification  and  gray  cast  iron  had  been  pro- 
duced in  the  first  instance.  In  other  words,  the  temper  carbon, 
although  in  a  very  finely  powdered  condition,  occupies  about  the 
same  amount  of  space  as  an  equal  weight  of  graphite,  and  causes 
about  the  same  ultimate  difference  in  size  between  the  original 
pattern  and  the  annealed  casting  as  when  gray  cast  iron  is  made. 
An  interesting  example  of  this  expansion  in  annealing  is  shown  in 
Fig.  274,  which  is  a  swivel  snap  for  hitching  straps.  Casting  No.  1 
is  first  poured,  cooled  and  cleaned.  It  is  then  embedded  in  the 


368 


THE   METALLURGY  OF   IRON   AND   STEEL 


sand  of  a  mold  and  casting  No.  2  is  poured  around  the  shank  of  it, 
as  shown  in  No.  3  of  Fig.  276.  Casting  No.  2  shrinks  upon  the 
shank  of  No.  1  so  as  to  make  a  close  fit,  and  no  swiveling  is  possi- 
ble, but  the  combined  casting  is  now  sent  to  the  annealing-ovens 
and  annealed.  This  causes  the  expansion  referred  to,  and  as  cast- 
ing No.  2  is  larger  in  diameter,  it  expands  the  more,  and  now  turns 
very  easily  around  the  shank  of  No.  1. 

Miscellaneous  Iron  Products.  — In  the  form  of  small  castings 
malleable  cast  iron  and  similar  products  often  masquerade  under 
the  name  of  steel,  because  under  that  name  the  producer  finds  a 

readier  market  for  them. 
On  account  of  their 
fluidity  they  may  be 
cast  very  cheaply  in 
small  sizes,  and  there- 
fore the  temptation  to 
use  them  as  a  material 
for  'cast-steel  hammers/1 
'hard-steel'  bevel  gears, 
'semi-steel  castings/  and 
even  automobile  'steel' 
drop-forgings,  is  a  strong 

one.  Engineers  are  warned  to  be  on  their  guard  against  a  de- 
ception of  this  kind,  for  legal  redress  has  been  sought  many 
times  in  vain.  A  clever  lawyer  may  easily  confuse  and  outwit 
a  judge  or  jury  with  the  involved  definitions  and  technical  de- 
scriptions necessary  to  make  the  distinction  clear.  It  is  usual 
for  the  manufacturer  when  putting  material  of  this  kind  upon 
the  market  to  qualify  the  name  'steel'  with  some  other  letters 
or  name,  such  as  '  P.  Q.  steel/  '  Smith  steel/  etc. ;  but  they  all  differ 
from  true  steel  in  that  they  were  not  "  cast  into  an  initially  malle- 
able mass."  Some  are  made  by  melting  a  large  proportion  of 
steel  with  cast  iron,  after  which  the  cooled  metal  may  or  may  not 
be  annealed  in  iron  oxide.  Others  are  made  by  a  long  or  thorough 
annealing  of  ordinary  malleable  castings  in  iron  oxide,  by  means 
of  which  the  metal  is  decarburized  to  some  depth,  and  is  then  car- 
burized  again  by  a  cementation  process.  This  makes  a  very  good 
material  for  some  purposes,  such  as  small  bevel  gears  not  requiring 

1  The  trade  would  ordinarily  understand  by  this  name  hammers  made  of 
crucible  steel,  so  the  use  of  this  name  is  really  a  fraud. 


FIGS.    274   TO    276. 


MALLEABLE  CAST  IRON  369 

strength  or  much  ductility,  but  it  ought  not  to  be  called '  steel/  If 
the  purpose  for  which  it  is  to  be  used  does  not  require  any  other 
properties  than  malleable  cast  iron  possesses,  then  it  should  be  used 
under  its  true  name;  but  if  it  is  to  be  used  under  circumstances 
where  it  is  liable  to  strain,  calling  it  'steel'  will  not  enable  it  to 
stand  up  under  the  work  any  better.  The  confusion  is  the  more 
easy  because  genuine  steel  is  made  by  the  cementation  of  wrought 
iron,  and  wrought  iron  goes  in  England  under  the  name  of  malle- 
able iron.  In  America  we  seldom  call  wrought  iron  '  malleable 
iron/  but  we  often  abbreviate  malleable  cast  iron  to  '  malleable 
iron/  or  even  to  '  malleable/ 


REFERENCES  ON  MALLEABLE  CAST  IRON 

See  90,  91,  92,  and  122. 

130.  Richard  Moldenke.  "Malleable  Castings,"  Parts  I,  II,  and 
III.  Instruction  Papers  Nos.  547A,  547B,  and  547C, 
of  the  International  Correspondence  Schools,  Scranton,  Pa. 
This  is  the  most  thorough  and  valuable  treatment  of  this 
subject  that  I  know  of. 


XIV 
THE  HEAT  TREATMENT  OF   STEEL 

WE  have  already  discussed  the  heat  treatment  of  cast  iron 
under  other  heads,  namely:  (1)  the  rapid  cooling  from  the  molten 
state,  or  'chilling/  and  (2)  the  annealing  of  malleable  cast  iron. 
Heat  treatment  is  of  much  greater  importance  in  connection  with 
steel,  because  nearly  99  per  cent,  of  all  the  steel  made  is  heated 
either  for  the  purpose  of  bringing  it  into  the  mobile  condition  in 
which  it  can  be  readily  wrought,  or  for  annealing.  Indeed,  the 
great  majority  of  steel  is  heated  several  times,  and  some  steel  is 
subjected  to  two  or  three  different  kinds  of  heat  treatment. 

IMPROPER  HEATING  OF  STEEL 

Overheating.  —  If  steel  be  heated  to  a  high  temperature,  say 
1100°  C.  (2010°  F.),  and  then  cooled  (either  slowly  or  rapidly) 
without  being  subjected  to  strain,  it  will  be  'coarse-grained'  as 
it  is  called,  that  is,  its  crystals  will  be  relatively  large  in  size. 
This  can  be  readily  seen  by  breaking  it  and  examining  the  frac- 
ture, which  will  be  bright  and  sparkling  if  the  crystals  are  coarse, 
or  dull-looking  and  fine-grained  if  they  are  small  (see  Fig.  284) . 
The  bright  fracture  is  technically  called  'crystalline'  or  'fiery/ 
while  the  fine-grained  one  is  called  'silky7  or  'sappy.'  The 
size  of  the  crystals  may  also  be  learned  with  great  accuracy  by 
means  of  the  microscope  (see  Figs.  277  to  282  and  286) .  Now,  if  the 
steel  which  was  coarse-grained  after  heating  to  1100°  be  heated 
instead  to  1200°,  the  crystals  will  be  still  larger  in  size;  if  heated 
to  1300°  they  will  be  larger  still,  and  so  on.  The  size  of  the  crys- 
tals will  depend  first  upon  which  of  these  high  temperatures  it 
was  heated  to,  and  second  upon  the  amount  of  carbon  it  contains. 
Low-carbon  steel  is  normally  larger  in  crystal-size  than  high- 
carbon  steel. 

Even  the  best  quality  of  steel,  if  rendered  coarse-grained  by 

370 


THE   HEAT  TREATMENT   OF   STEEL  371 

'  overheating/  will  suffer  in  its  valuable  properties,  and  may  be- 
come quite  unfit  for  use.  Medium-  and  high-carbon  steel  will 
lose  both  strength  and  ductility;  low-carbon  steel  will  lose  strength 
even  up  to  50  per  cent,  of  the  original,  but  does  not  seem  to  be 
materially  damaged  in  ductility  unless  the  overheating  is  con- 
tinued for  a  long  time  or  at  a  very  high  temperature. 

Cure  for  Overheating.  —  Let  our  first  example  be  steel  con- 
taining 0.9  per  cent,  carbon,  that  is,  steel  consisting  entirely  of 
pearlite.  If  this  be  heated  from  some  point  below  the  line  P  SK 
in  Fig.  246,  page  314,  to  some  point  above  that  line,  a  new  crys- 
tallization will  begin,  and  all  traces  of  previous  crystallization 
will  disappear.  It  seems  as  if  dissolving  the  ferrite  and  cementite 
in  each  other  produces  forces  which  obliterate  almost  all  existing 
crystalline  forms.  So,  if  this  particular  steel  has  been  made 
coarse-grained  by  overheating,  we  may  make  that  grain  fine 
again  by  reheating  the  steel  from  below  the  line  P  SK  to  just 
above  it.  This  process  is  known  as  '  restoring/  or,  by  some  writ- 
ers, '  refining '  the  steel.  It  is  an  operation  which  should  be  thor- 
oughly understood  by  every  metallurgist  and  engineer.  When  we 
reheat  the  steel  we  must  be  careful  not  to  go  to  a  high  tempera- 
ture again,  for  a  new  crystal-size  is  born  at  the  line  P  SK,  and 
the  crystals  grow  with  every  increase  in  temperature.  The  re- 
searches of  Professors  Howe  and  Sauveur  1  indicate  that  the  size 
of  the  crystals  is  almost  directly  proportional  to  the  temperature 
reached  above  the  line  PSK.  If,  therefore,  we  barely  cross  the 
line,  we  will  obtain  the  smallest  grain-size  that  the  steel  is  capable 
of  (see  Fig.  281). 

The  cure  for  coarse  crystallization  in  steel  with  less  than  0.9 
per  cent,  carbon  is  to  reheat  it  from  below  the  line  PS  K  to  above 
the  line  GO S,  at  which  the  last  of  the  ferrite  goes  into  solution. 
That  is  to  say,  the  correct  temperature  for  restoring  the  grain- 
size  will  depend  upon  the  amount  of  carbon  in  the  steel;  low- 
carbon  steel  must  be  heated  to  nearly  900°  C.  (1650°  F.) ;  0.4  per 
cent,  carbon  steel  must  be  heated  to  nearly  800°  C.  (1470°  F.); 
and  so  on.2  We  can  never  get  as  small  a  grain-size  in  steel  with 

1  See  page  246  of  No.  1,  page  8. 

2  It  is  to  be  remembered  that  the  changes  indicated  by  the  lines  in  Fig. 
246  occur  at  a  higher  temperature  on  heating  than  on  cooling  (see  page  312); 
so  it  is  well  to  heat  the  steel  about  25°  C.  higher  than  the  points  on  those 
lines. 


FIG.   277.  — NO.    1A.     STEEL   OF   0.05 

PER  CENT.   CARBON   ROLLED. 

Magnified  40  diameters. 


FIG.   278. —  NO.    IB.      STEEL   OF  0.50 

PER  CENT.  CARBON  ROLLED. 

Magnified  60  diameters. 


FIG.  279.  —  NO.  2A.     SAME  AS  NO.  1A 

OVERHEATED  TO  1420°  C.  (2588°  F.) 

Magnified  40  diameters. 


FIG.  280.  —  NO.  2B.    SAME  AS  NO.  IB. 

OVERHEATED  TO  1420°  C.  (2588°  F.) 

Magnified  60  diameters. 


FIG.  281.  —  NO.  3A.    SAME  AS  NO.  2A. 

REHEATED  SLIGHTLY  ABOVE  AC8. 

Magnified  40  diameters. 


FIG.  282.  —  NO.  3B.    SAME  AS  NO.  2B. 

REHEATED  SLIGHTLY  ABOVE  AC3-3. 

Magnified  60  diameters. 


Series  A  by  F.  C.  Wallower  in  the  Metallographic  Laboratory  of  Columbia  University, 
Department  of  Metallurgy. 

Series  B  by  G.  Rocour  in  the  Metallographic  Laboratory  of  Columbia  University,  De- 
partment of  Metallurgy. 


THE   HEAT  TREATMENT  OF   STEEL  373 

less  than  0.9  per  cent,  carbon  as  we  can  in  that  which  is  exactly 
0.9  per  cent,  carbon,  because  a  new  grain-size  begins  to  grow 
after  we  have  crossed  the  line  PS  K,  and  yet  we  cannot  entirely 
eliminate  the  old  grain-size  until  we  cross  the  line  G  0  S.  Where 
the  lines  GOS  and  PSK  are  near  together  (say,  with  0.7  per 
cent,  carbon),  the  new  grain-size  does  not  have  much  chance  to 
grow  before  the  restoration  is  complete,  and  therefore  we  may 
obtain  steel  with  a  pretty  small  grain;  but  where  they  are  far 
apart  (as  in  the  low-carbon  steels)  the  restoration  can  never  be 
very  thorough,  because  we  have  to  go  so  far  above  PSK  to  ob- 
literate the  old  grain-size  that  the  new  grain-size  will  have  at- 
tained ample  proportions.  But  the  evidence  seems  to  show  that 
the  best  net  result  is  obtained  by  going  just  above  the  line  GOS 
in  all  cases. 

In  the  case  of  steel  with  more  than  0.9  per  cent,  carbon  a  some- 
what similar  condition  exists:  we  must  reheat  the  steel  above 
the  line  S  a  in  order  to  produce  complete  elimination  of  the  previ- 
ous grain-size,  but  a  new  grain-size  begins  to  grow  from  the  cross- 
ing of  the  line  PSK.  But  here  we  disregard  the  line  Sa,  and 
restore  our  steels  in  every  case  by  reheating  them  over  the  line 
PSK,  just  as  in  the  case  of  pure  pearlite.  The  reason  for  this  is 
that  the  lines  Sa  and  PSK  diverge  so  rapidly  that  we  have  to 
heat  very  far  above  the  line  PSK  before  we  cross  S  a,  and  there- 
fore the  new  grain-size  has  grown  greatly.  Furthermore,  the 
only  object  of  heating  above  the  line  Sa  is  to  take  the  excess 
cementite  into  solution;  for  the  ferrite  and  cementite  in  the 
pearlite  all  went  into  solution  as  soon  as  we  crossed  the  line 
PSK,  but  the  amount  of  excess  cementite  is  always  small  in 
proportion,  and  therefore  in  its  influence  on  restoration.  Even 
with  steel  containing  2  per  cent,  of  carbon  the  excess  cementite 
is  only  16  per  cent.  This  is  different  from  the  low-carbon  steels, 
where  the  excess  ferrite  will  be  usually  over  80  per  cent. 

Evidence  of  Overheating.  —  A  piece  of  steel  may  be  heated 
many  times  above  the  line  PSK  and  cooled  again,  but  obviously 
only  the  latest  heating  will  leave  its  impression  on  the  structure, 
because  each  crossing  of  the  line  on  the  way  up  removes  the  effect 
of  previous  heat  treatment.1  The  relation  between  the  size  of 


is  only  true  in  a  qualified  sense,  in  that  the  previous  overheating 
must  not  have  been  very  close  to  the  melting-point.  We  shall  discuss  this 
point  under  the  head  of  "  Burning."  Indeed,  even  where  burning  has  not 


374  THE  METALLURGY  OF   IRON  AND   STEEL 

the  crystals  and  the  temperature  above  PS K  is  so  constant  that 
we  may  determine  what  this  temperature  was  from  the  analysis 
of  the  steel  and  an  examination  of  the  grain.  To  do  this  it  is 
usually  necessary  to  get  a  piece  of  steel  of  the  same  analysis, 
heat  different  pieces  of  it  to  various  temperatures,  and  compare 
(see  page  380).  The  analysis  must  be  approximately  the  same 
not  only  in  carbon  but  also  in  phosphorus,  sulphur,  silicon,  and 
manganese,  as  well  as  in  any  alloying  elements,  if  present,  such  as 
nickel,  chromium,  tungsten,  etc.,  because  all  of  them  have  an 
effect  upon  the  size  of  grain  and  also  upon  the  change  in  size  of 
grain  by  overheating.  Generally,  it  is  not  important  to  know 
the  exact  temperature  of  overheating,  but  only  whether  or  not 
overheating  in  some  degree  has  occurred;  and  this  is  not  difficult 
to  prove,  because  almost  all  who  use  steel  are  familiar  with  the 
normal  fracture  of  steels  of  different  carbon  and  can  tell  at  a 
glance  if  the  grain  is  large;  those  who  are  not  so  familiar  with  its 
appearance  may  easily  become  so.  The  grain  being  large  is  proof 
that  overheating  was  the  cause,  provided  chemical  analysis  shows 
everything  about  normal,  especially  phosphorus  and  silicon. 

Steel  members  of  bridges  or' other  structures  sometimes  break 
and  disclose  a  crystalline  fracture  which  is  often  attributed  to  the 
effect  of  vibration.  The  same  thing  occurs  with  points  or  shanks 
of  rock  drills  and  similar  implements.  It  is  the  more  general 
opinion  among  metallurgists  that  the  crystalline  fracture  in  all 
these  cases  is  due  to  faulty  heat  treatment  during  manufacture, 
and  especially  to  finishing  the  forging  or  rolling  while  the  tem- 
perature is  still  too  high.  The  manufacturers  of  steel  like  to 
maintain  the  opposite  opinion,  for  obvious  reasons,  but  I  do  not 
know  of  there  ever  having  been  any  reliable  proof  offered  that  vi- 
bration had  caused,  or  is  capable  of  causing,  large-sized  grain  in 
steel.  It  may  be  possible,  but  the  more  we  learn  about  the  sub- 
ject the  more  we  are  inclined  to  believe  that  improper  manufac- 
ture is  the  cause,  and  that  the  grain  was  large  before  the  steel  was 
put  in  service,  although  its  nature  was  not  disclosed  until  the 
break  occurred. 

Mechanical  Cure  for  Overheating.  —  When  steel  is  to  be  rolled 

occurred,  a  skillful  microscopist  may  sometimes  discern  the  effect  of  over- 
heating after  the  steel  has  been  restored  by  reheating;  because,  although  the 
crystals  are  all  small,  they  are  arranged  in  groups  which  show  the  form  of  the 
previous  large  crystals. 


THE   HEAT  TREATMENT  OF   STEEL  375 

or  forged  it  is  frequently  heated  to  a  temperature  of  1100°  to 
1350°  C.  (2010°  to  2460°  F.),  and  it  might  be  thought  that  this 
treatment  would  seriously  damage  it.  So  it  would,  but  for  the 
fact  that  the  subsequent  mechanical  pressure  upon  the  metal 
breaks  down  the  crystals  and  reduces  them  again  to  a  small  size. 
The  result  is  that  the  final  size  of  the  crystals  is  dependent  upon 
the  temperature  of  the  material  at  the  finish  of  the  mechanical 
operation.  In  other  words,  steel  finished  at  900°  C.  (1650°  F.) 
has  a  finer  structure  than  the  same  steel  if  finished  at  1100°  C. 
(2010°  F.).  We  do  not  feel  warranted  in  stating  numerically  the 
exact  relation  between  the  finishing  temperature  and  the  grain- 
size,  as  we  have  not  yet  sufficient  evidence,  but  several  rules  af- 
fecting the  final  size  of  grain  seem  to  be  virtually  established:  (1) 
It  is  more  advantageous  to  have  the  mechanical  work  applied 
continuously  from  the  highest  temperature  employed  down  to 
the  finishing  temperature,  rather  than  to  have  long  waits  during 
which  the  steel  cools;  and  especially  is  this  true  when  the  amount 
of  work  put  upon  the  metal  at  the  lower  temperatures  is  small. 
In  other  words,  if  the  steel  is  formed  roughly  to  shape  and  size 
at  a  high  heat,  is  then  allowed  to  cool,  and  a  little  work  is  done 
upon  it  at  the  lower  temperature,  the  grain  will  not  be  good. 

(2)  It  is  best  for  the  metal  to  be  worked  by  several  passes  through 
the  rolls,  or  many  blows  of  the  hammer,  rather  than  to  effect  the 
same  amount  of  reduction  by  a  lesser  number  of  heavy  drafts. 

(3)  The  greater  the  amount  of  reduction  the  better;  that  is,  to 
work  a  large  piece  down  to  the  desired  article  gives  a  better 
structure.     (4)  The  best  temperature  at  which  to  finish  the  work 
it  probably  upon,  or  slightly  below,  the  lines  G-O-S  or  S-K  in  Fig. 
246,  page  314. 

Action  in  Rolling.  —  The  exact  crystalline  action  that  takes 
place  under  mechanical  treatment  is  not  definitely  known.  In 
the  case  of  rolling  Professor  Howe  has  tentatively  assumed  the 
conditions  graphically  shown  in  Fig.  283,1  in  which  the  line  DG 
represents  the  size  of  grain  at  the  different  temperatures.  At 
1400°  C.  (2550°  F.)  the  grain-size  is  represented  by  the  distance 
of  the  line  from  the  axis  0-0.  On  the  first  passage  through  the 
rolls  the  grains  are  crushed  to  a  very  small  size,  but  on  emerg- 
ing again  they  grow  very  rapidly.  Meanwhile,  however,  the  metal 
has  been  cooled,  and  this  fact,  as  well  as  the  inability  of  the  grains 
1  Page  263  of  No.  1,  page  8. 


376 


THE  METALLURGY  OF   IRON  AND   STEEL 


to  grow  instantly,  causes  the  new  size  of  grain  to  be  smaller  than 
before.  Therefore,  each  passage  through  the  rolls  renders  the 
crystals  smaller  in  size,  the  final  size  depending  upon  the  tempera- 
ture and  the  amount  of  pressure  in  the  last  pass.  The  only 


1400  C 

(2552  F) 


(1274  F) 


=  Diameter  of  grain  at  this  finishing  temperature 


32°F 


18345 

Diameter  of  Grain 
FIG.  283.     From  Howe,  "Iron.  Steel  and  other  Alloys." 

abnormal  assumption  in  this  argument  is  that  the  crystals  grow 
rapidly  after  the  crushing,  whereas  we  know  that  when  steel  is 
heated  to  any  of  these  high  temperatures,  the  growth  is  relatively 
slow.  This  objection  is  not  strong  enough  alone  to  refute  the  theory, 
but  other  hypotheses  may  be  advanced  for  those  who  require 
further  explanation.  For  example,  it  may  be  supposed  that  the 
steel  is  so  mobile  at  the  very  high  temperatures  that  it  yields  to 


THE  HEAT  TREATMENT   OF   STEEL  377 

distortion,  not  altogether  by  the  crushing  of  the  crystals,  but  by 
the  sliding  of  the  crystals  past  one  another;  as  the  temperature 
becomes  lower,  however,  the  mobility  of  the  mass  becomes  less, 
and  less  sliding  is  possible,  so  that  more  crushing  of  the  crystals 
takes  place. 

Finishing  Temperatures.  —  William  Campbell  has  studied  the 
finishing  temperature  of  steel  containing  0.5  per  cent,  carbon 
and  finds  that  the  very  best  qualities  are  produced  in  the  steel 
if  mechanical  work  is  ended  just  at  the  time  when  ferrite 
begins  to  separate  from  solid  solution,  that  is  to  say,  just  when 
the  steel  is  below  the  line  G-O-S  in  Fig.  246,  page  314.  Work 
below  that  temperature  greatly  increases  the  brittleness  of  the 
material,  while  finishing  the  work  at  a  higher  heat  results  in  lower 
strength.  Upon  the  evidence  at  hand,  we  may  tentatively  as- 
sume like  conditions  for  steels  of  any  carbon,  and  expect  the  best 
results  if  mechanical  work  is  ended  when  the  steel  is  at  a  tem- 
perature which  brings  it  exactly  upon  the  line  G-O-S  or  S-K,  but 
reserving,  perhaps,  the  right  to  change  this  statement  slightly 
when  more  data  are  obtained. 

Welding.  —  This  brings  us  to  the  subject  of  welding,  or  the 
joining  of  two  pieces  of  wrought  iron  or  steel  by  pressing  or  ham- 
mering them  together  while  at  a  very  high  temperature.  In  this 
way  a  joint  may  be  made  which  cannot  be  seen  by  the  eye  unless 
the  steel  is  polished  and  etched  with  acid,  which  usually  develops 
the  junction  line  very  clearly.  The  exact  temperature  of  welding 
is  not  known,  but  probably  it  is  very  near  the  melting-point,  when 
the  steel  is  in  a  soft  and  almost  pasty  condition.  Low-carbon  steel 
welds  most  easily;  moreover,  all  impurities,  especially  silicon  and 
sulphur,  reduce  weldability.  The  procedure  in  welding  is  very 
simple,  and  consists  in  heating  the  two  pieces  that  are  to  be  welded 
to  a  high  temperature,  dissolving  off  the  iron  oxide,  and  then 
pressing  the  two  pieces  together  forcibly.  The  dissolving  off  of 
the  oxide  is  usually  accomplished  by  rubbing  the  metal  in  some 
flux,  such  as  borax.  At  the  present  time  various  patented  '  weld- 
ing plates'  are  sold.  These  consist  of  thin  plates  of  flux  which 
are  put  between  the  two  pieces  to  be  welded  and  so  get  rid  of  the 
oxide,  the  pieces  being  hammered  together  with  the  plate  between 
them. 

In  the  actual  manipulation  for  welding  the  two  pieces  that  are 
to  be  joined  together  are  usually  'upset/  or  in  some  way  en- 


378  THE   METALLURGY  OF   IRON   AND   STEEL 

larged  in  size,  so  that  after  the  junction  the  part  of  the  bar  right 
at  the  weld  is  larger  in  size  than  the  remainder.  This  part  is 
then  hammered  continuously  until  the  metal  is  at  a  red  heat, 
the  object  being  to  break  up  the  coarse  crystals  produced  by 
the  high  temperature,  and,  by  having  a  low  'finishing  tempera- 
ture/ to  obtain  a  small  grain-size.  With  proper  welding  this 
object  will  be  attained  so  far  as  the  metal  immediately  adja- 
cent to  the  weld  is  concerned,  but  there  is  always  a  spot  within 
six  inches  or  so  of  the  weld  which  must  necessarily  have  been  over- 
heated without  subsequently  receiving  mechanical  treatment,  i.e., 
'  hammer  refining/  down  to  the  proper  finishing  temperature.  Thus 
it  is  that  most  welded  pieces  break  at  a  point  not  far  from  the 
junction  and  under  a  strain  much  less  than  the  original  strength 
of  the  bar.  Blacksmiths  and  experienced  welders  are  wont  to 
declare  that  if  a  welded  bar  does  not  break  in  the  weld  itself,  then 
it  must  be  as  strong  as  the  original  metal.  As  I  have  shown,  how- 
ever, this  is  by  no  means  true.  In  a  welding  test  carried  on  with 
great  care  in  this  country  by  skilful  and  experienced  welders  who 
were  placed  upon  their  mettle,1  the  strength  and  elastic  limit  of 
the  welded  bar  was  almost  never  as  great  as  the  original  bar,  and 
in  some  cases  was  less  than  half.  In  ductility  even  worse  results 
were  obtained.  In  a. similar  test  carried  on  at  the  Royal  Prussian 
Testing  Institute  the  average  strength  of  welded  bars  of  medium 
steel  was  only  58  per  cent,  of  the  original,  that  of  softer  steel  only  71 
per  cent.,  and  of  puddled  iron  only  81  per  cent.,  while  the  poorest 
results  were  only  23,  33,  and  62  per  cent,  respectively.  It  was 
seen  that  bad  crystallization  adjacent  to  the  weld  was  the  cause 
of  ihe  damage. 

This  evidence  shows  positively  that  welded  steel  and  iron 
bars  should  always  be  reheated  to  a  temperature  just  above  the 
line  G-O-S  in  order  to  restore  by  heating  the  grain-size  of  all  parts. 

Burning.  —  In  the  vernacular  of  the  trade,  all  overheated 
steel  is  termed  'burnt/  but  this  is  not  correct  usage,  because  true 
burning  takes  place  only  when  the  overheating  is  most  abusive, 
and,  indeed,  when  the  metal  is  heated  almost  to  its  melting-point. 
It  is  probable  that  steel  is  burnt  only  when  it  is  heated  above  the 
line  A-a  in  Fig.  246,  page  314.  Alfred  Stansfield  has  studied 
this  question  very  ably,2  and  distinguishes  three  stages  of  burn- 
ing. The  first  stage  is  reached  when  the  steel  barely  crosses  the 
1  See  pages  401  to  406  of  No.  2,  page  8.  2  See  No.  143,  page  395. 


THE   HEAT  TREATMENT   OF   STEEL 


379 


line  A-a,  that  is,  when  the  first  drops  of  melted  metal  begin  to 
form  in  the  interior  of  the  mass:  they  segregate  to  the  joints  be- 
tween the  crystals  and  cause  weakness.  Stansfield  thinks  that 
steel  burned  only  to  this  stage  may  be  restored  by  reheating 
it  first  to  a  high  temperature,  cooling,  and  then  heating  again 
to  a  temperature  just  above  the  lines  G-O-S-K.  The  second 
stage  in  burning  is  reached  when  these  liquid  drops  segregate  as 
far  as  the  exterior  and  leave  behind  a  cavity  filled  with  gas. 


FIG.  284.  —  METCALF  TEST.  FRACTURES  OF  STEEL  CONTAINING  ONE  PER 
CENT.  OF  CARBON. 

Stansfield  thinks  that  steel  burned  to  this  stage  might  be  re- 
stored by  combined  reheating  and  forging.  As  a  matter  of 
safety,  however,  I  believe  it  would  be  well  to  remelt  all  such  ma- 
terial; in  other  words,  send  it  to  the  scrap  pile.  The  third  and 
last  stage  of  burning  is  reached  when  gas  collects  in  the  interior 
of  the  metal  under  sufficient  pressure  to  break  through  the  skin 
and  project  liquid  steel,  which  produces  the  well-known  scintil- 
lating effect  at  this  temperature.  Into  the  openings  formed  by 
these  minute  explosions  air  enters  and  oxidizes  the  interior. 
There  can  be  no  remedying  of  steel  which  has  been  burned  to  this 
extent. 


380  THE   METALLURGY   OF   IRON   AND   STEEL 

Metcalf  Test.  —  A  very  interesting  experiment  is  the  "  Met- 
calf  test,"  originated  by  William  Metcalf.1  It  is  best  performed 
upon  a  bar  of  high-carbon  steel,  because  this  material  shows  the 
differences  in  structure  so  readily  to  the  eye.  A  bar  of  steel  about 
12  in.  long  is  notched  with  a  hacksaw  or  chisel  at  intervals  of 
an  inch.  One  end  is  then  placed  in  a  fire  and  heated  to  a  tem- 
perature at  which  it  scintillates,  while  the  other  end  is  at  a  black 
heat.  Then  it  is  removed  and  cooled.  It  is  immaterial  whether 
the  cooling  be  rapid  or  slow,  but  time  may  be  saved  by  plunging 
it  into  water.  It  is  then  broken  at  every  notch,  and  an  exam- 
ination of  the  fractures  will  show  a  very  large  size  of  crystals  at 
the  end  which  is  burnt,  gradually  decreasing  until  a  fine  and 
silky  appearance  is  presented  where  the  metal  was  exactly  at 
the  temperature  of  restoration,  while  beyond  that  point  the 
fracture  will  be  the  same  as  that  of  the  original  bar.  In  case 
this  test  is  made  upon  low-carbon  .steel  it  should  not  be  notched 
before  treatment,  but  afterwards  it  should  be  cut  apart  with  a 
hacksaw  at  intervals  of  an  inch,  and  then  polished  and  examined 
under  the  microscope,  because  soft  steel  will  not  break  with- 
out bending,  and  this  bending  destroys  the  indications  of  the 
fracture.  This  Metcalf  test  is  very  serviceable  in  case  we  desire 
to  compare  steel  that  we  suspect  of  being  overheated  with  over- 
heated steel  of  like  analysis  to  determine  the  degree  of  over- 
heating. 

Castings  do  Not  Burn.  —  It  might  be  thought  that  every  steel 
casting  would  suffer  the  injuries  due  to  burning  because  it  is 
cooled  through  the  space  between  the  lines  A-B  and  A-a,  and  es- 
pecially so  in  the  case  of  high-carbon  steel,  which  is  very  easy  to 
burn,  on  account  of  the  low  temperature  at  which  this  line  A-a 
occurs  and  of  the  long  distance  between  the  two  lines.  Such 
injury,  however,  does  not  ordinarily  take  place,  anol  this  fortu- 
nate circumstance  is  explained  partially  by  each  of  three  differ- 
ences between  the  heating  and  cooling  of  steel:  (1)  When  steel  is 
heated  into  the  area  where  burning  takes  place,  it  is  subjected 
longer  to  the  burning  temperature,  because  it  generally  takes 
longer  to  heat  steel  than  to  cool  it.  (2)  When  steel  is  being 
heated,  the  heat  is  traveling  inward  from  the  outside,  and  there- 
fore all  parts  are  expanding,  and  there  is  some  opportunity  for  the 
crystals  to  draw  apart  and  form  cavities.  On  the  other  hand, 
1  See  pp.  405,  406  (especially  406)  of  No.  116,  page  332. 


THE   HEAT  TREATMENT   OF   STEEL  381 

when  it  is  cooling  from  the  molten  state,  the  outside  layers  are 
the  cooler,  and  tend  to  contract  upon  the  interior  and  hold  the 
crystals  more  firmly  together.  (3)  When  steel  is  cooling  from 
a  molten  state,  it  is  constantly  giving  off  from  solution  hydrogen 
and  other  deoxidizing  gases  which  are  soluble  in  it  while  liquid, 
and  these  gases  prevent  the  oxidation  of  the  crystal  faces  by  the 
percolation  of  air  into  the  interior. 

Ingotism.  —  I  have  already  discussed  ingotism  and  said  that 
the  crystals  in  cast  steel  are  larger  than  those  of  rolled  steel,  due 
to  growth  while  the  metal  is  at  a  high  temperature,  and  I  have 
stated  that  sometimes  these  crystals  are  very  large,  because  the 
conditions  of  casting  cause  the  steel  to  occupy  a  longer  time  in 
cooling  from  the  liquid  state  down  to  a  black  heat.  It  is  prob- 
able that  ingots  and  castings  do  not  show  the  effects  of  overheat- 
ing (ingotism)  to  any  marked  extent  unless  they  are  a  long  time 
above  1100°  C.  (2010°  F.).  In  case  these  coarse  crystals  do  form, 
they  may  be  restored  to  some  extent  by  reheating  the  casting 
to  a  point  just  above  the  line  G-O-S.  Why  ingotism  is  not  com- 
pletely remedied  by  the  same  treatment  that  cures  the  coarse 
crystallization  due  to  overheating,  I  am  unable  to  say,  unless  it 
be  that  ingotism  is  accompanied  by  burning  to  at  least  a  slight 
extent. 

Stead's  Brittleness.  —  In  addition  to  the  damage  caused  by 
overheating,  steel  very  low  in  carbon  (say  under  0.15  per  cent.) 
is  subject  to  another  and  peculiar  danger,  for  if  this  soft  steel 
be  held  for  a  very  long  time  at  temperatures  between  500°  and 
750°  C.  (930°  and  1380°  F.),  the  crystals  become  enormous  and 
the  steel  loses  a  large  part  of  its  strength  and  ductility.  Fortu- 
nately it  takes  a  very  long  time,  in  fact  days,  to  produce  this 
effect  to  any  alarming  degree,  so  that  it  is  not  liable  to  occur, 
even  through  carelessness,  during  manufacture  or  mechanical 
treatment.  But  steel  is  sometimes  placed  in  positions  where  it 
may  suffer  this  injury,  for  example,  in  the  case  of  the  tie-rods  of 
furnaces,  supports  for  boilers,  etc.,  so  that  the  danger  should  be 
borne  in  mind  by  all  engineers  and  users  of  steel.  I  recall  an 
instance  where  the  breaking  of  a  piece  of  chain  that  supported 
one  side  of  a  50-ton  open-hearth  ladle  caused  a  loss  of  life  under 
the  most  horrifying  conditions,  due  to  the  fact  that  the  wrought- 
iron  chain  had  been  heated  up  many  times  to  a  temperature  above 
500°  C.  (930°  F.),  and  had  finally  reached  a  condition  of  coarse 


382  THE  METALLURGY  OF   IRON  AND  STEEL 

crystallization,  so  that  it  was  unable  to  bear  the  strain  upon  it 
when  the  ladle  was  full  of  metal. 

This  phenomenon  of  coarse  crystallization  in  low-carbon  steel 
is  known  as  "Stead's  brittleness,"  after  J.  E.  Stead,  who  has 
explained  its  cause.  The  effect  seems  to  begin  at  a  temper- 
ature of  about  500°  C.,  and  proceeds  more  and  more  rapidly  with 
an  increase  in  temperature  until  we  reach  750°  C.,  above  which 
no  growth  seems  to  take  place.  The  damage  may  be  repaired 
completely  by  heating  the  steel  just  above  the  line  G-0.  In  other 
words,  the  remedy  for  coarse  crystallization  in  this  case  is  the 
same  as  that  for  coarse  crystallization  due  to  overheating,  and 
all  steel  which  is  placed  in  positions  where  it  is  liable  to  reach 
these  temperatures  frequently,  should  be  restored  at  intervals 
of  a  week  or  a  month,  or  as  often  as  may  be  necessary. 

HARDENING  OF  STEEL 

If  steel  be  raised  to  a  bright-red  heat  and  then  rapidly  cooled, 
as,  for  example,  by  plunging  it  into  water,  it  becomes  very  much 
harder  and  at  the  same  time  stronger  and  more  brittle.  One  cir- 
cumstance is  absolutely  necessary  to  produce  the  increase  in 
hardness,  namely,  that  the  temperature  from  which  rapid  cooling 
takes  place  shall  be  above  the  critical  temperature  of  the  steel. 
Take,  for  example,  steel  containing  0.9  per  cent,  carbon;  we  may 
heat  this  ever  so  little  below  the  point  S  in  Fig.  246,  page  314, 
and  no  increase  in  hardness  will  take  place,  even  though  we  cool 
with  extreme  rapidity.  On  the  other  hand,  if  we  cool  the  same 
steel  rapidly  from  ever  so  little  above  the  point  S,  it  will  be  hard 
enough  to  scratch  glass  and  brittle  enough  to  fly  into  pieces  under 
a  blow  of  the  hammer.  This  is  the  maximum  practical  hardness 
which  can  be  obtained,  for  if  we  quench  the  steel  at  a  still  higher 
temperature,  the  only  result  of  importance  is  to  do  it  damage  by 
increasing  its  grain-size.  In  case  we  have  less  than  0.9  per  cent, 
carbon  in  our  steel,  the  best  temperature  for  hardening  is  just 
above  the  line  G-O-S,  because  that  gives  the  maximum  hardness 
and  also  the  best  grain-size.  The  best  temperature  from  which 
to  harden  steel  with  more  than  0.9  per  cent,  carbon  is  just  above 
the  line  S-K,  because  that  gives  the  best  grain  structure,  although 
it  is  true  that  greater  hardness  is  obtained  if  we  cool  from  above 
the  line  S-a. 


THE   HEAT  TREATMENT  OF   STEEL  383 

Carbon  and  Hardness.  —  The  hardness  of  steel  increases  with 
every  increase  of  carbon.  This  applies  to  the  hardness  of  steel 
in  its  natural  state,  and  still  more  influentially  to  its  hardness 
after  the  treatment  I  have  just  described.  Although  iron  free 
from  carbon  is  hardened  by  rapid  cooling  from  above  the  point 
Ac2  (760°  C.  =  1400°  F.),  and  a  little  more  so  when  rapidly  cooled 
from  above  AcB  (900°  C.  =  1650°  F.),  yet  this  degree  of  hardness 
is  so  slight  as  to  be  perceptible  only  by  means  of  delicate  labora- 
tory tests.  With  0.25  per  cent,  carbon  the  hardness  begins  to  be 
perceptible  by  crude  tests,  but  it  is  only  when  we  get  above  0.75 
per  cent,  carbon  that  ordinary  steel  acquires  sufficient  hardness 
for  the  process  to  be  used  commercially, — for  example,  for  springs, 
saws,  etc.  Metal-cutting  tools  are  usually  made  of  steel  con- 
taining 1  per  cent,  or  so  of  carbon,  while  very  hard  implements, 
such  as  files,  etc.,  will  contain  1.5  per  cent.,  or  slightly  more. 

Rate  of  Cooling  and  Hardness.  —  The  degree  of  hardness  of 
steel  also  varies  with  the  speed  of  cooling  from  above  the  critical 
range  of  temperature.  When  the  cooling  is  very  slow,  as,  for 
example,  when  it  takes  several  days  to  cool,  the  steel  will  be  as 
soft  as  it  is  possible  to  make  it.  When  it  is  cooled  by  being  taken 
out  of  the  furnace  and  suspended  in  the  air,  or  thrown  upon  a  sand 
floor,  it  will  still  be  relatively  soft.  When  cooling  is  still  more 
rapid,  as,  for  example,  when  it  is  taken  out  of  the  furnace  at  a 
bright-red  heat  and  plunged  into  a  heavy  oil  with  a  low  conduct- 
ing power  for  heat,  it  becomes  quite  hard  and  springy,  provided 
its  carbon  is  in  the  neighborhood  of  0.8  per  cent,  or  above. 
Quenching  in  a  thin  oil  from  the  same  temperature  makes  it  still 
harder.  Quenching  in  water  makes  it  harder  still ;  and  so  on,  the 
degree  of  hardness  increasing  as  we  quench  in  liquids  which  take 
the  heat  away  from  it  faster  and  faster,  such  as  ice-water,  ice- 
brine,  ice  sodium  chloride  solution,  and  mercury  near  its  freezing- 
point  (-39°  C.  =  -38°F.). 

Theories  of  Hardening.  —  One  essential  feature  of  hardening 
is  that  the  steel  must  be  heated  to  a  temperature  above  the  line 
P-S-K,  that  is  to  say,  to  a  point  where  at  least  some  of  the  solid 
solution  of  iron  and  carbon  is  formed.  There  are  several  different 
theories  to  explain  the  hardness  produced  by  rapid  cooling  from 
this  point,  the  two  most  important  being  the '  carbon  theory '  and 
the  'allotropic  theory/  Both  of  these  theories  depend  upon  the 
following  line  of  reasoning:  At  temperatures  above  the  critical 


384  THE  METALLURGY  OF  IRON  AND  STEEL 

range  the  molecules  of  steel  are  in  a  hard  condition.1  As  they  cool 
from  this  point  and  cross  the  critical  range  of  temperature,  the 
molecules  change  from  the  hard  state  to  a  soft  state,  but  this 
change  is  not  rapid  and  requires  time  for  its  accomplishment; 
rapid  cooling  does  not  afford  the  necessary  time,  and  so  perpetuates 
the  hard  state  of  the  molecules.  This  line  of  reasoning  leaves  only 
one  point  in  doubt,  namely,  what  causes  the  molecules  to  be  hard 
when  the  steel  is  above  the  critical  temperature,  i.e.,  when  iron 
and  carbon  are  dissolved  in  each  other? 

The  Carbon  Theory.  —  The  carbon  theory  assumes  that  the 
hardness  of  steel  is  due  altogether  to  the  carbon  dissolved  in  it, 
and  in  evidence  its  advocates  point  to  the  extreme  hardness  of 
one  form  of  carbon  —  the  diamond.  This  theory  has  the  ad- 
vantage of  simplicity,  and  has  in  its  favor  the  fact  that  the  hard- 
ness varies  almost  directly  with  the  amount  of  carbon.  Against 
the  theory,  it  is  urged  that  the  amount  of  carbon  is  really  too  small 
to  produce  such  a  great  degree  of  hardness  in  the  whole  mass  of 
metal.  Furthermore,  although  carbon  is  found  in  many  metals, 
it  does  not  confer  hardness  on  any  of  them  except  iron. 

The  Allotropic  Theory.  —  We  have  already  learned  that  in 
the  solid  solution  the  iron  is  present  in  the  gamma  allotropic  form, 
and  there  is  one  school  of  metallurgists  which  attributes  the  hard- 
ness to  the  allotropic  form  of  iron  alone  and  denies  that  carbon 
has  any  direct  influence.  It  has  been  shown,  by  very  delicate 
laboratory  tests  on  iron  practically  free  from  carbon,  that  the 
gamma  and  beta  allotropic  modifications  are  harder  than  the 
alpha  modification.  He  was  not  able  to  show  how  great  was  the 
increase  of  hardness  of  one  form  over  another,  because  he  was 
never  able  to  cool  the  iron  fast  enough  to  prevent  it  changing 
back  in  part  to  the  alpha  form.  In  the  absence  of  carbon  the 
change  from  gamma  to  beta  and  from  beta  to  alpha  is  very  rapid, 
so  that  cooling  has  to  be  almost  instantaneous  in  order  to  prevent 
it,  and  this,  of  course,  is  impossible.  The  '  allotropists '  explain  the 

1  It  is  difficult  for  some  to  understand  how  molecules  of  steel  can  be  in  a 
hard  condition  at  a  temperature  at  which  we  know  that  the  mass  as  a  whole 
is  soft  and  mobile;  but  this  can  be  explained  by  the  following  comparison: 
A  ball  of  wet  sand  and  clay  is  soft  and  mobile  as  a  whole,  because  the  particles 
move  by  each  other  readily  and  the  mass  changes  its  shape  under  pressure; 
yet  the  individual  particles  composing  this  mass  are  many  of  them  hard 
enough  to  scratch  glass  with  ease. 


THE  HEAT  TREATMENT   OF   STEEL  385 

greater  hardness  of  high-carbon  steel  as  compared  with  low-carbon 
steel  upon  the  basis  that  the  presence  of  carbon  makes  the  change 
from  gamma  to  beta  and  to  alpha  iron  slower,  and  therefore  enables 
more  of  the  iron  to  be  retained  in  the  gamma  and  beta  forms  by 
the  rapid  cooling. 

One  additional  argument  in  favor  of  the  allotropic  theory  is 
that  when  steel  cools  slowly  through  the  critical  range,  it  loses 
its  hardness  slightly  before  the  carbon  comes  out  of  solution. 
This  would  indicate  that  the  allotropic  change  took  place  before 
the  carbon  change,  and  that  the  allotropic  change  was  the  cause 
of  hardness.  What  is  true  of  the  loss  of  hardness  is  also  true  of 
the  other  physical  changes  which  take  place  at  the  same  time. 
That  is  to  say,  the  steel  regains  its  magnetism,  decreases  in  electric 
resistance,  and  increases  in  thermo-electric  power  in  a  large  part 
before  much  carbon  is  separated  from  solution. 

Influence  of  Carbon  on  Hardness.  —  I  think  no  one  to-day 
denies  that  the  carbon  in  steel  has  a  very  important  influence 
upon  its  hardness,  even  though  it  may  not  be  the  sole  cause  of  it. 
This  influence  is  twofold:  (1)  We  have  stated  that  the  changes 
that  take  place  when  steel  is  cooled  through  the  critical  range 
were  not  rapid  changes,  and  for  this  reason  fast  cooling  was  able 
in  part  to  prevent  their  taking  place.  Carbon  has  the  effect  of 
making  these  changes  still  slower,  and  so  increasing  the  effect  of 
the  rapid  cooling.  Howe  calls  this  the  'brake  action'  of  carbon. 
(2)  The  more  the  carbon  in  solid  solution,  the  harder  will  that 
solid  solution  be. 

The  Compromise  Theory.  —  Several  theories  have  been  ad- 
vanced which  are  a  compromise  between  that  of  'the  carbonists' 
and  that  of  'the  allotropists.;  The  simplest  of  these,  and  the 
theory  now  most  generally  accepted,  is  that  the  hardness  of  the 
molecules  of  steel  above  the  critical  range  is  due  partly  to  the 
allotropic  form  in  which  the  iron  exists,  and  partly  to  the  fact  that 
we  have  a  solid  solution  of  iron  and  carbon.1  In  other  words, 


1  Where  I  speak  of  a  solution  of  carbon  and  iron,  I  intend  to  include  under 
this  also  the  solution  of  iron  and  a  carbide  of  iron.  That  is  to  say,  we  have 
two  substances,  iron  and  carbon,  and  they  are  dissolved  in  each  other.  It 
may  be  that  the  carbon  is  united  with  part  of  the  iron  to  form  a  carbide,  and 
then  that  this  carbide  is  dissolved  in  the  rest  of  the  iron;  but  I  use  the  term 
"solid  solution  of  iron  and  carbon"  to  cover  either  this  condition  or  that  of 
elemental  carbon  dissolved  in  iron. 


386  THE  METALLURGY  OF   IRON  AND   STEEL 

the  hardness  is  due  to  the  fact  that  we  have  a  solid  solution  of 
carbon  in  an  allotropic  form  of  iron. 

The  Internal  Stress  Theory.  —  There  is  an  entirely  independent 
theory  of  the  hardness  of  steel  which  attributes  it,  not  to  the  re- 
tention of  a  hard  molecule  existing  above  the  critical  range,  but 
to  stresses  set  up  in  the  metal  by  rapid  cooling  through  the  crit- 
ical range.  That  such  stresses  exist  cannot  be  doubted,  for  some- 
times the  rapid  cooling  of  high-carbon  steel  causes  it  to  break  into 
pieces,  or  to  open  up  a  cavity  in  the  middle  from  end  to  end, 
but  the  theory  itself  does  not  seem  sufficient  to  explain  all  the 
facts. 

Tempering.  —  Hardened  steel  is  too  brittle  to  be  used  without 
some  degree  of  tempering;  except  for  a  small  variety  of  purposes, 
such  as  the  points  of  armor-piercing  projectiles,  the  face  of  armor 
plate,  etc.  In  order  to  understand  just  what  tempering  does, 
let  us  consider  the  exact  condition  of  hardened  steel:  it  is  in  a 
hard  and  brittle  condition  which  is  not  natural  to  it  at  atmos- 
pheric temperatures,  but  which  has  been  brought  down  with  it 
from  a  higher  temperature  by  means  of  rapid  cooling.  Theo- 
retically, when  the  temperature  fell  below  690  C°.  (1272°  F.), 
the  molecules  of  steel  should  have  changed  over  to  the  soft  form. 
Their  hard  condition  is  not  in  equilibrium  at  the  lower  tempera- 
ture, in  the  same  sense  that  ice  is  not  in  equilibrium  in  hot  weather. 
Why,  then,  does  not  the  steel  change  back  into  the  soft  form? 
Ice,  if  given  time  enough,  will  all  change  into  water  when  the 
temperature  is  above  0°  C.  (32°  F.).  The  reason  the  change  does 
not  take  place  in  the  steel  after  we  have  cooled  it  to  the  atmos- 
pheric temperature  is  that  the  mass  as  a  whole  becomes  too  rigid 
and  immobile  at  the  lower  temperature  to  permit  any  alteration 
in  its  molecules  to  take  place. 

However,  it  is  only  necessary  to  decrease  this  rigidity  in  order 
to  permit  a  slight  change.  For  example,  if  a  piece  of  hardened 
steel  be  kept  in  boiling  water  for  some  days  it  will  lose  a  part  of  its 
hardness;  if  it  be  heated  a  little  more,  it  will  lose  more  hardness 
and  lose  it  much  more  quickly.  Each  loss  in  hardness  is  accom- 
panied by  a  loss  in  brittleness  as  well.  If  it  be  heated  to  about 
200°  C.*(392°  F.),  quite  a  little  of  the  brittleness  will  be  lost  and 
a  part  of  the  hardness.1  It  is  now  in  condition  to  be  used  for  steel 

1  After  the  heating  it  is  immaterial  whether  cooling  is  fast  or  slow,  as  the 
same  result  will  be  produced. 


THE  HEAT  TREATMENT  OF   STEEL  387 

engraving  tools,  lathe  tools,  and  other  implements  to  cut  metals. 
If  we  heat  to  250°  C.  (480°  F.),  we  again  temper,  and  to  a  point 
where  the  steel  is  still  less  brittle  and  will  withstand  greater 
strains,  but  is  at  the  same  time  sufficiently  hard  to  be  used  for 
rock  drills,  penknives,  stone-cutting  tools,  and  so  forth.  If  tem- 
pered to  275°  C.  (525°  F.),  the  steel  has  not  even  yet  lost  so  much 
brittleness  as  to  be  able  to  withstand  a  great  deal  of  shock,  or 
even  bending,  but  is  still  hard  enough  to  be  suitable  for  dental 
and  surgical  instruments,  swords,  needles,  hacksaws,  etc.  Wood- 
saws,  the  majority  of  springs,  and  other  articles  that  must  be 
ductile  even  at  the  expense  of  hardness,  will  be  tempered  to  a 
temperature  of  about  300°  C.  (570°  F.),  which  is  the  greatest  de- 
gree of  tempering  that  is  ordinarily  employed. 

It  is  interesting  to  note  that  when  hardened  steel  is  tempered, 
the  physical  changes  produced  by  the  tempering  —  the  decrease 
in  hardness  and  brittleness,  increase  in  electric  conductivity,  etc. 
—  precede  the  separation  of  carbon  from  the  solid  solution.  By 
tempering  we  may  lose  70  per  cent,  of  the  hardness,  93  per  cent, 
of  the  electric  resistance,  and  nearly  100  per  cent,  of  the  thermo- 
electric power  produced  in  the  steel  by  the  hardening  operation, 
when  only  13  per  cent,  of  the  carbon  has  been  changed  from  the 
dissolved  form. 

Temper  Colors.  —  Nature  has  provided  a  ready  means  of  de- 
termining the  temperature  of  steel  between  200°  and  300°  C. 
(390°  and  570°  F.)  without  the  aid  of  thermometers  or  other  in- 
struments; and,  since  this  is  the  range  of  temperatures  in  which 
practically  all  of  the  tempering  of  hardened  steel  takes  place,  this 
provision  is  a  most  fortunate  one.  It  comes  about  through  the 
oxidation  of  the  metal  at  those  different  points.  At  200°  C. 
(390°  F.)  a  thin  film  of  oxide  forms  upon  the  steel,  but  is  not  suf- 
ficient to  entirely  hide  the  white  color  underneath,  so  that  the 
combination  produces  a  light  lemon  color.  As  the  temperature 
rises  the  film  of  oxide  becomes  thicker  and  the  yellow  color  darker 
until,  at  about  225°  C.  (437°  F.),  it  has  changed  to  orange.  At 
250°  C.  the  orange  has  changed  to  a  pink  which  is  known  as 
'  pigeon  wing/  At  275°  C.  the  pigeon  wing  has  turned  into  a  light 
purple,  which,  at  300°  C.,  becomes  a  blue. 

Hardening,  Tempering  and  Annealing.  —  Only  quenching  in 
water,  or  in  some  other  medium  which  takes  the  heat  away  as  fast 
or  faster,  goes  under  the  name  of  hardening.  Quenching  in  oil, 


388  THE  METALLURGY  OF   IRON   AND   STEEL 

melted  lead,  etc.,  cools  the  steel  less  rapidly  and  makes  it  less  hard 
and  less  brittle  than  quenching  in  water,  so  to  this  operation 
the  name  of  'tempering'  is  given.     Cooling  in  the  air,  in  sand,' 
in  the  furnace,  or  by  any  other  slow  method,  is  called  'annealing.7 

Combined  Hardening  and  Tempering.  —  If  steel  be  cooled  from 
above  the  critical  range  by  quenching  in  some  slow  conducting 
liquid  in  the  first  instance,  as  in  cylinder  oil,  the  same  intermediate 
hardening  and  embrittling  effect  will  be  produced  upon  it  as  if  it 
were  first  hardened  in  water  and  then  tempered  a  certain  amount. 
Therefore  the  quenching  in  oil  and  similar  mediums  has  come  to 
be  called  'tempering.'1  Another  method  of  combining  hardening 
and  tempering  after  only  one  heating  is  used  in  the  tempering  of 
the  cutting  edges  of  chisels  and  similar  tools:  the  end  of  the  tool 
is  first  heated  just  above  the  critical  range,  and  then  the  extreme 
point  only  is  quenched  in  water  until  it  is  black,  after  which  it  is 
withdrawn  and  rubbed  bright  upon  a  piece  of  sandpaper,  or  upon 
a  brick.  This  is  done  merely  to  give  a  bright  surface  upon  which 
to  observe  the  play  of  temper  colors.  The  heat  from  the  shank 
now  begins  to  creep  down  into  the  point,  which  takes  the  various 
temper  colors  in  order,  beginning  with  the  lemon.  When  the 
desired  degree  of  tempering  is  reached  —  say,  the  pigeon- wing 
color  —  the  whole  tool  is  put  into  water.  This  is  merely  to  '  put 
out  the  fire'  and  stop  more  heat  coming  down  into  the  tempered 
point ;  it  has  nothing  to  do  with  the  tempering  operation  itself. 

Annealing.  —  If  hardened  steel  be  heated  to  a  temperature 
of  600°  C.  (1100°  F.)  its  pristine  softness  and  ductility  is  returned 
to  it.  This  process  is  known  as  'annealing.'  As  a  general  thing 
we  do  not  anneal  at  as  low  a  temperature  as  this  because  we  not 
only  desire  to  make  the  steel  soft,  but  also  to  give  it  as  small 
a  grain-size  as  possible,  and  this  is  done  by  heating  just  above 
the  lines  G-O-S-K  in  Fig.  246,  page  314.  Therefore  the  temper- 

1  Strictly  speaking  this  is  a  misnomer,  and  very  bad  usage,  but  like  so 
many  incorrect  terms  that  have  become  current  in  the  iron  and  steel  trade,  it 
is  now  too  firmly  established  to  be  displaced.  The  error  in  terms  has  gone 
even  further  than  this,  and  the  hardness  of  steel  is  known  as  its  'temper,' 
while  making  it  softer  is  known  as  'drawing  its  temper.'  To  temper  means 
literally  to  soften,  to  mollify;  or  else  to  mitigate  one  quality  with  another 
(as  justice  is  said  to  be  'tempered'  with  mercy).  Either  of  these  meanings  is 
quite  correct  when  we  'temper'  hardened  steel  by  heating  it  slightly,  but  is 
just  the  opposite  when  we  call  hardening  steel  in  oil  'tempering,'  or  when  we 
speak  of  'drawing  a  temper.' 


THE   HEAT  TREATMENT   OF   STEEL  389 

atures  just  above  these  lines  are  not  only  the  hardening  and  re- 
storing temperatures,  but  the  annealing  temperatures  as  well,  if 
we  cool  slowly.  It  is  only  when  we  have  a  steel  with  a  structure 
already  fine  that  we  use  the  low-temperature  annealing,  as,  for 
example,  with  cold-rolled  steel,  wire,  etc.  To  heat  such  steel 
above  the  line  G-O-S  would  not  increase  its  softness  and  would 
undo  some  of  the  benefit  of  the  cold  work. 

Magnetism  and  the  Lines  G-O-S-K.  —  It  will  be  remembered 
that  iron  is  present  in  the  solid  solution  in  the  gamma  allotropic 
form,  and  therefore  the  solid  solution  is  non-magnetic.  Therefore 
all  the  steels  to  the  right  of  the  point  0  in  Fig.  246,  page  314,  lose 
the  last  of  their  magnetism  at  the  same  time  as  they  cross  the 
lines  0-S-K.  These  steels  comprise  all  containing  0.4  per  cent, 
of  carbon  and  more.  To  harden,  anneal  or  restore  such  steels  we 
may  guide  our  work  of  heating  by  means  of  an  ordinary  horse- 
shoe magnet,  which  makes  a  most  accurate  and  simple  tool. 
Let  the  magnet  hang  outside  of  the  furnace  and  take  the  steel  out 
at  intervals  to  test  it.  When  it  no  longer  attracts  the  magnet, 
begin  to  cool  it.  For  steels  with  less  than  0.4  per  cent,  carbon  we 
can  use  the  magnet  to  tell  us  when  the  temperature  corresponding 
to  the  line  M-0  is  reached,  for  all  iron  loses  its  magnetism  at  that 
point,  and  then  it  is  a  comparatively  simple  matter  to  judge  by 
eye  the  relatively  short  temperature  intervals  above  that  point 
which  it  is  necessary  for  the  steel  to  traverse  before  it  crosses  the 
line  G-0.  If  this  method  is  followed  I  think  it  will  be  found  in 
many  works  that  annealing  temperatures  have  been  much  too 
high,  and  that  better  steel  will  be  obtained  in  future.  We  do  not 
get  the  steel  any  softer  by  annealing  it  hotter,  but  only  by  slower 
cooling. 

THE  CONSTITUENTS  OF  HARDENED  AND  TEMPERED  STEELS 

It  is  now  pretty  generally  admitted  by  metallurgists  that  aus- 
tenite  is  the  solid  solution  of  gamma  iron  and  carbon.  When 
this  cools  slowly  through  the  critical  range  it  decomposes  into 
ferrite  and  cementite.  It  is  also  very  generally  admitted  that  the 
decomposition  does  not  take  place  spasmodically,  but  progresses 
by  stages,  and  many  believe  that  the  substances  identified  under 
the  microscope  as  martensite,  troostite,  and  sorbite  are  the  prod- 
ucts of  these  stages.  That  is  to  say,  martensite  is  the  first  stage 


390  THE   METALLURGY  OF   IRON  AND  STEEL 

of  decomposition  of  austenite,  troostite  is  the  second,  sorbite  is 
the  third,  and  pearlite  is  the  consummation.  If  this  is  so,  then 
austenite  will  be  found  in  the  steels  cooled  with  the  greatest  ra- 
pidity, martensite  will  be  found  in  those  cooled  with  the  next  de- 
gree of  rapidity,  troostite  will  be  found  in  the  next  intermediate 
steels,  sorbite  in  the  next,  and  pearlite  in  those  slowly  cooled. 
To  this  extent,  indeed,  the  facts  agree  with  the  argument,  but 
hardly  any  dare  predicate  further  too  positively  from  this  evi- 
dence alone.  Our  knowledge  upon  this  whole  subject  is  still  very 
new,  and  though  a  small  army  of  workers  is  busy  collecting  evi- 
dence and  interpreting  it  as  best  they  can,  all  our  present  state- 
ments must  necessarily  be  made  tentatively,  with  the  idea  of  pre- 
senting the  facts  so  that  they  may  be  of  some  practical  benefit, 
even  though  later  information  may  oblige  us  to  change  slightly 
the  scientific  basis  upon  which  we  found  them. 

Austenite.  —  Austenite  can  be  obtained  at  atmospheric  tem- 
peratures in  ordinary  carbon  steels  only  when  three  conditions 
are  collectively  present:  (1)  The  brake  action  of  carbon  must  be 
very  strong,  that  is,  there  must  be  above  1.1  per  cent,  of  carbon 
present;  (2)  the  steel  must  be  cooled  with  the  greatest  rapidity, 
as  by  quenching  it  in  iced  solutions  at,  or  a  few  degrees  below 
zero  C.;  and  (3)  it  must  be  cooled  from  above  1000°  C.  (1830°  F.). 
Even  then  austenite  cannot  be  preserved  throughout  the  whole 
mass  of  the  steel,  but  at  least  a  part  of  it  will  be  decomposed  to 
the  stage  represented  by  the  martensite  structure  (see  Fig.  288) 
while  cementite  will  separate  also  if  the  carbon  is  very  high.  Un- 
der the  microscope  austenite  may  be  differentiated  from  marten- 
site  by  its  white  color  after  etching  with  a  10-per-cent.  solution  of 
hydrochloric  acid.  Better  results  are  obtained  if  the  etching  is 
aided  by  electrolysis,  the  steel  being  made  the  anode,  or  positive 
pole,  and  a  piece  of  platinum  being  made  the  cathode.  Austenite 
is  not  a  very  important  constitutent  practically,  because  prob- 
ably it  almost  never  occurs  in  commercial  steels.  It  is  imme- 
diately decomposed  into  later  stages  upon  tempering. 

Martensite.  —  Martensite  is  the  chief  constituent  of  ordinary 
hardened  steels,  that  is,  of  steels  quenched  from  above  the  critical 
range  in  water  or  in  an  iced  solution.  Its  structure  is  shown  in 
Fig.  288.  It  is  even  harder  than  austenite,  for  a  steel  needle  drawn 
across  the  surface  of  a  polished  piece  of  steel  will  scratch  the  aus- 
tenite plainly  without  making  a  mark  upon  the  martensite.  Its 


FIG.  285.  —  NO.   1A.      STEEL    OF    0.34 
PER  CENT.  CARBON  OVERHEATED 
TO  ABOUT  1300°  C.  (2372°  F.). 
Magnified  250  diameters. 


FIG.  286.  —  NO.  2A.     SAME  AS  NO.  1A. 

REHEATED  SLIGHTLY  ABOVE  AC3. 

Magnified  250  diameters. 


FIG.   287. —STEEL   OF    1    PER   CENT. 
CARBON   BURNT. 

Magnified  265  diameters. 


FIG.    288.  —  MARTENSITE. 
Magnified  250  diameters. 


FIG.   289.  —  MARTENSITE   (WHITE) 

AND   TROOSTITE    (DARK). 
Magnified    500    diameters.     Etched   lightly 
with  tincture  of  iodine.     (H.  C.  Boynton.) 


FIG.  290.  —  AUSTENITE  (WHITE)  AND 

TROOSTITE  (DARK). 
Magnified  60  diameters.     Steel  of  1.41  per 

cent,   carbon.     Etched  with  picric  acid. 

(William  Campbell.) 


392 


THE  METALLURGY  OF   IRON  AND   STEEL 


structure  is  developed  by  the  'polish  attack '  method  of  F.  Os- 
mond (see  p.  453).  Martensite  is  also  found  very  largely  in  the 
tempered  steels,  to  which  they  doubtless  owe  their  quality  of 
hardness.  It  was  long  thought  to  be  the  solid  solution  itself,  and 
is  still  spoken  of  as  such  in  several  books  upon  the  subject;  but 
the  microscope  shows  positively  that  it  is  not  free  from  some 
decomposition. 

Hardenite.  —  Hardenite  is  the  name  sometimes  given  to  '  sat- 
urated martensite/  that  is,  martensite  containing  0.9  per  cent, 
carbon.  It  is  often  found  in  German  and  French,  and  occasion- 
ally in  English  and  American  books. 

Troostite.  —  Troostite  is  obtained  in  either  of  three  ways :  (1) 
By  quenching  steel  in  water  when  it  has  cooled  just  to  the  line 
P-S-K  in  Fig.  246,  page  314;  (2)  by  quenching  steel  from  a  higher 
temperature  in  boiling  water,  oil,  or  some  other  of  the  tempering 
mediums;  and  (3)  by  hardening  in  the  usual  way  and  then  tem- 
pering by  reheating.  In  other  words,  troostite  is  a  product  of  the 
usual  tempering  operations,  and  is  found  abundantly  in  tempered 
steels.  Under  the  microscope  it  may  be  distinguished  by  the 

' polish  attack'  (page  453)  or 
by  etching  with  tincture  of 
iodine.  It  appears  as  yellow, 
brown,  blue  or  black  color- 
ations on  the  borders  of  the 
martensite,  and  often  between 
the  martensite  and  sorbite. 
The  division  between  it  and 
the  martensite  is  very  sharp, 
but  it  shades  very  gradually 
into  the  sorbite  (Figs.  289, 290). 
Sorbite.  —  Sorbite  is  very 
close  to  pearlite,  and  differs 
from  it  chiefly  in  that  the 
crystals  of  ferrite  and  cemen- 
tite  are  not  quite  perfectly 
developed  and  segregated  from 

one  another  (see  Fig.  291).  It  might  at  first  seem  almost  like 
splitting  hairs  to  differentiate  between  the  two,  but  this  is  not  so. 
because  of  the  importance  of  sorbite,  due  to  its  having  greater 
strength  than  pearlite.  Pearlite  has  a  finer  and  more  intimately 


FIG.    291.  — FERRITE    AND   SORBITE 
IN    RAILED   STEEL. 

Magnified  250  diameters. 
Etched  with  picric  acid. 


THE   HEAT  TREATMENT   OF   STEEL  393 

entangled  structure  than  any  other  slowly  cooled  steel,  and  to 
this  we  attribute  the  fact  that  pure  pearlite  steel  (0.9  per  cent, 
carbon)  is  stronger  than  any  other.  But  the  structure  of  sorbite 
is  even  finer  than  that  of  pearlite,  and  sorbitic  steels  are  corre- 
spondingly stronger  than  pearlitic  steels. 

Sorbite  may  be  obtained  by  quenching  the  steel  immediately 
below,  or  just  at  the  end,  of  cooling  through  the  critical  range, 
or  by  cooling  the  steel  pretty  fast  through  the  critical  range  with- 
out actually  quenching,  or  by  rapid  cooling  and  then  reheating 
to  about  600°  C.  (1110°  F.). 

Osmondite.  —  Only  very  recently  what  is  apparently  another 
constituent  of  hardened  and  tempered  steels  has  been  discovered, 
and  to  this  the  name  of  'osmondite'  has  been  given.  It  would 
seem  that  osmondite  is  a  solid  solution  of  carbon  (or  of  a  carbide 
of  iron)  in  the  alpha  allotropic  modification  of  iron.  It  is  there- 
fore an  anomaly,  and  can  only  exist  in  equilibrium  momentarily, 
so  to  speak,  because  the  normal  solid  solution  contains  the  iron  in 
the  gamma  allotropic  form.  It  would  seem,  however,  that  when 
this  gamma  solid  solution  decomposes,  it  passes  through  a  phase 
wherein  the  iron  has  changed  from  the  gamma  to  the  alpha  form, 
before  the  precipitation  of  the  ferrite  occurs.  In  other  words, 
then,  osmondite  is  simply  another  stage  in  the  decomposition  of 
austenite  into  pearlite.  It  differs  from  the  other  stages  by  having 
a  definite  constitution  and  nature,  whereas  martensite,  troostite 
and  sorbite  are  more  or  less  indefinite  and  uncertain  in  compo- 
sition, being  in  fact  probably  a  mixture  of  two  or  more  constitu- 
ents rather  than  definite  and  individual  components. 

It  is  evident  that  osmondite  can  never  compose  the  whole  of 
any  piece  of  steel,  because  the  earlier  stages  of  the  austenite  de- 
composition will  grade  into  it  on  the  one  side  and  the  later  stages 
on  the  other.  That  is  to  say,  we  would  not  expect  that  the  entire 
piece  of  steel  would  change  simultaneously  and  instantaneously 
from  austenite  into  osmondite,  and  then  likewise  from  osmondite 
to  pearlite.  Osmondite  may  be  obtained  by  tempering  hardened 
steel  at  400°  C.  (750°  F.),  but  its  distinguishment  under  the  micro- 
scope is  not  known  at  present.  Our  chief  means  of  recognizing 
it  are  by  the  fact  that  it  causes  the  steel  to  dissolve  more  rapidly 
in  dilute  sulphuric  acid  and  to  be  colored  more  deeply  by  alcoholic 
hydrochloric  acid,  and  by  the  fact  that  steel  containing  a  good 
deal  of  osmondite  has  lost  a  major  part  of  all  the  qualities  given 


394 


THE  METALLURGY  OF   IRON  AND   STEEL 


to  it  by  hardening,  although  almost  all  the  carbon  is  still  in  the 
solid  solution. 

It  is  to  be  noted  that  the  evidence  proving  the  existence  of 
osmondite  is  still  open  to  the  possibility  of  doubt,  although  the 
probabilities  are  greatly  in  favor  of  it. 

Summary.  —  We  may  summarize  the  constituents  of  har- 
dened and  tempered  steels  in  the  following  table,  which  is  adapted 
from  one  designed  by  Howe: 

STAGES  OF  THE  TRANSFORMATION  FROM  AUSTENITE  INTO  PEARLITE 


CONSTITUTION 


Austenite 

Martensite,  a  transition  substance. 

Troostite,  a  transition  substance .  . 


Osmondite 

Sorbite,  a  transition  substance. . . 


Pearlite. 


Solid  solution  of  an  iron  carbide  in  gamma 
iron. 

The  next  step.  Some  of  the  gamma  iron 
is  changed  to  beta  and  to  alpha  iron. 
It  is  harder  than  austenite. 

The  third  step.  The  quantity  of  gamma 
and  beta  iron  constantly  decreasing, 
that  of  alpha  iron  constantly  increas- 
ing. 

Solid  solution  of  iron  carbide  in  alpha 
iron. 

A  mixture  of  a  constantly  decreasing 
quantity  of  osmondite  with  a  con- 
stantly increasing  quantity  of  pearlite, 
too  fine  to  be  resolved  by  the  micro- 
scope. 

A  conglomerate,  or  a  mechanical  mixture 
of  free  alpha  iron  (alpha  ferrite)  with 
the  iron  carbide,  Fe3C,  cementite. 


In  a  very  illuminating  discussion  of  the  constitution  of  iron 
carbon  alloys,1  Albert  Sauveur  predicates  that  when  steel  cools 
slowly  through  the  critical  range  and  there  takes  place  the  de- 
composition of  austenite  —  the  solid  solution  of  carbon  and 
gamma  iron  —  it  first  changes  into  a  solid  solutiorr  of  carbon  and 
beta  iron,  thence  into  a  solid  solution  of  carbon  and  alpha  iron, 
and  thence  into  cementite  and  alpha  iron.  In  other  words, 
Sauveur  considers  that,  instead  of  the  solid  solution  decom- 
posing by  the  precipitation  of  its  gamma  ferrite,  which  im- 
mediately changes  to  beta  and  then  to  alpha  ferrite,  the  fer-^ 
rite  in  the  solid  solution  is  changed  from  gamma  to  beta  and 
then  to  alpha,  after  which  the  precipitation  occurs.  By  the 


Journ.  Iron  and  Steel  Inst.,  No.  4,  1906,  pp.  493-575. 


THE  HEAT  TREATMENT  OF   STEEL  395 

light  of  recent  researches  this   theory   of    Sauveur's  is   greatly 
strengthened. 


REFERENCES  ON  THE  HEAT  TREATMENT  OF  STEEL 

140.  Report  of  the  Alloys  Research  Committee  of  the  Institution  of 

Mechanical  Engineers  (England).  Minutes  of  the  Proceed- 
ings. Report  No.  1,  October,  1891;  No.  2,  April,  1893; 
No.  4,  February,  1897;  No.  5,  February,  1899;  No.  6, 
January  and  February,  1904;  No.  7,  November  and 
December,  1905. 

141.  Joseph  V.  Woodworth.     "Hardening,  Tempering,  Annealing, 

and  Forging  of  Steel."  New  York,  1903.  This  book  tells 
much  of  the  practice  and  manipulation  of  these  operations. 

142.  John  Lord  Bacon.     "Forge  Practice  (Elementary)."     New 

York,  1904.  This  book  also  deals  largely  with  practice 
and  manipulation. 

143.  Alfred  Stansfield.     "The  Burning  and  Overheating  of  Steel." 

Journal  Iron  and  Steel  Institute,  No.  11,  1903,  pages  433- 
468. 

144.  Carl  Benedicks.     "Recherches  Physiques  et  Physico-Chimi- 

ques  sur  PAcier  au  Carbone."  Upsala,  1904.  With  a 
good  bibliography. 

145.  Hanns  Freiherr  von  Jliptner.     "Siderology,  the   Science  of 

Iron."     Translated  by  Charles  Salter,  London,  1902. 

146.  Hanns  Freiherr  von  Jiiptner.     "  Grundzuege  der  Siderologie." 

In  three  volumes.  Vol.  i,  "  The  Constitution  of  Iron  Alloys 
and  Slags,"  Leipzig,  1900;  vol.  ii,  "Relation  Between  the 
Thermal  and  Mechanical  Changes,  Constitution  and  Proper- 
ties of  Iron  Alloys,"  1902;  vol.  iii,  "The  Influence  of 
Impurities;  the  Manufacture  of  Iron  and  Steel,"  etc. 

147.  J.   W.   Mellor.     "The   Crystallization   of   Iron  and   Steel." 

London,  1905.  This  is  a  very  clear  and  readily  intelligible 
discussion  of  the  heat  treatment  of  steel,  and  an  introduc- 
tion to  metallography. 

148.  George  W.  Ailing.     "Points  for  Buyers  and  Users  of  Tool 

Steel."  New  York,  1903.  Being  a  general  review  of  the 
main  sources  of  trouble  and  how  to  avoid  them. 


XV 

ALLOY    STEELS 

WE  have  already  described  ordinary  steel  (which  to  distinguish 
it  from  the  so-called  alloy  steels  is  often  known  as  '  carbon  steel ') 
as  an  alloy  of  iron  and  carbon,  and  it  is  impossible  to  consider  it 
otherwise  with  equal  accuracy.  But  there  is  another  class  of 
materials  to  which  the  specific  name  of  ' alloy  steels'  is  applied. 
This  comprises  steels  to  which  a  controlling  amount  of  some  alloy- 
ing element  in  addition  to  the  carbon  is  added. 

Definitions.  —  The  International  Committee  upon  the  nomen- 
clature of  iron  and  steel  defines  alloy  steels  as  "those  which  owe 
their  properties  chiefly  to  the  presence  of  an  element  (or  elements) 
other  than  carbon."  The  distinction  between  an  element  added 
merely  to  produce  a  slight  benefit  to  ordinary  carbon  steel  and  the 
same  element  added  to  produce  an  alloy  steel  is  sometimes  a  very 
delicate  one.  For  example,  manganese  is  added  in  amounts  usu- 
ally less  than  1.50  per  cent,  to  all  Bessemer  and  open-hearth  steels 
for  the  sake  of  getting  rid  of  oxygen  and  neutralizing  the  effect  of 
sulphur.  Likewise  silicon  is  sometimes  added  in  amounts  of  0.1 
to  0.2  per  cent,  to  get  rid  of  blow-holes.  But  neither  of  these 
additions  produce  what  is  known  as  an  alloy  steel.  When  we 
make  '  manganese  steel '  containing  10  to  20  per  cent,  manganese, 
the  material  has  new  properties  quite  different  from  the  same 
steel  without  manganese  and  we  therefore  get  an  alloy  steel. 
Similarly  '  silicon  steel '  containing  2  or  3  per  cent,  of  silicon  will 
have  an  entirely  new  set  of  properties  due  to  the  silicon,  and  will 
therefore  become  an  alloy  steel. 

Ternary  Alloys.  —  A  ternary  alloy,  or  three-part  alloy,  is  an 
alloy  composed  of  iron,  carbon,  and  one  other  influential  element. 
This  class  includes  the  alloy  steels  which  are  used  most  abundantly 
by  man  and  the  most  important  of  which  are  nickel  steel,  man- 
ganese steel,  chrome  steel,  tungsten  steel,  molybdenum  steel, 
.silicon  steel,  vanadium  steel,  and  titanium  steel.  There  are  sev- 


ALLOY   STEELS  397 

eral  other  ternary  steels  which  have  been  investigated  and  used  to 
a  small  extent,  such  as  boron  steels,  cobalt  steels,  etc.  The  field 
of  useful  ternary  steels  has  not  yet  been  investigated  except  in 
the  most  meager  degree  and  a  wide  scope  is  left  for  future  in- 
ventors. There  are  many  elements  whose  influence  on  steel  has 
not  yet  been  studied,  and  even  among  those  which  are  commonly 
used,  there  are  some  of  which  only  limited  proportions  have  been 
employed. 

Quarternary  Steels.  —  Quarternary,  or  four  part,  steels  consist 
of  iron,  carbon,  and  two  other  alloying  elements.  The  commonest 
and  most  important  of  these  are  nickel-chromium  steels,  tungsten- 
manganese  and  tungsten-chromium  steels,  nickel-manganese, 
manganese-silicon,  tungsten-molybdenum,  tungsten-nickel,  nickel- 
vanadium  steels,  etc.,  etc.  The  result  produced  by  adding  an 
alloying  element  to  ordinary  carbon  steel  is  astonishing  and  inca- 
pable of  being  predicated,  arid  that  obtained  by  a  combination  of 
two  alloying  elements  is  far  more  so.  New  products  result  with 
properties  entirely  different,  and  in  some  cases  almost  the  opposite, 
of  those  of  its  constituents,  so  that  almost  any  combination  at  ran- 
dom may  lead  to  a  surprise,  even  when  the  effect  of  different  com- 
binations of  the  same  components  is  known.  Therefore  the  possi- 
bilities of  quarternary  steels  seem  to  be  very  great  and  the  field 
has,  as  yet,  hardly  been  touched. 

Manufacture  of  Alloy  Steels.  —  The  manufacture  of  alloy  steels 
is  usually  very  simple  and  calls  for  no  special  comment  here.  As  a 
general  thing  the  alloying  element  is  added  like  the  recarburizer. 
For  example,  in  the  manufacture  of  manganese  steel  the  requisite 
amount  of  f erro-manganese  will  be  added  at  the  end  of  the  process ; 
in  the  manufacture  of  nickel  steel  we  may  add  ferro-nickel  in  the 
same  way,  but  it  is  more  common  here  to  add  shotted-nickel  during 
the  process  and  allow  it  to  dissolve  in  the  steel  bath  and  remain 
there  until  the  metal  is  tapped;  tungsten  steels  and  tungsten- 
chrome  steels  are  often  made  by  the  crucible  process  and  the 
requisite  amount  of  ferro-chrome  and  ferro-tungsten,  or  of  me- 
tallic chromium  and  metallic  tungsten,  is  placed  on  top  of  the 
charge  when  the  crucible  is  filled. 

The  treatment  of  some  of  the  alloy  steels  is  not  so  simple: 
Nickel  steel  may  be  heated,  rolled  and  forged  without  any  great 
precaution,  but  these  operations  are  performed  upon  manganese, 
tungsten,  and  some  of  the  other  alloy  steels  only  after  great  diffi- 


398  THE  METALLURGY  OF  IRON  AND  STEEL 

culty  and  experience.     Under  the  head  of  these  different  steels,  I 
shall  describe  the  proper  method  of  treatment. 


NICKEL  STEELS 

Nickel  steels  are  the  most  important  of  all  the  alloy  steels 
and  are  the  most  abundantly  used.  In  the  ordinary  commercial 
alloys  the  nickel  ranges  from  1.50  to  4.50  per  cent,  and  usually 
from  3.00  to  3.75  per  cent,  while  the  carbon  is  usually  from  0.20 
to  0.50  per  cent.  Not  counting  armor-plate,  which  is  really 
a  quarternary  steel,  containing  both  nickel  and  chromium,  the 
most  important  uses  of  nickel  steel  are  for  structural  work  in 
bridges,  railroad  rails,  especially  on  curves,  steel  castings,  ord- 
nance, engine  forgings,  shafting,  especially  marine  shafting, 
frame  and  engine  parts  for  automobiles,  wire  cables,  axles,  es- 
pecially for  automobiles  and  railroad  cars,  etc.,  etc.  We  can 
best  learn-  the  reasons  for  these  particular  uses  by  discussing 
the  distinctive  properties  conferred  by  the  nickel  and  their  use- 
fulness. 

Tensile  Properties.  —  The  chief  distinction  between  nickel 
steel  and  carbon  steel  is  the  higher  elastic  limit  of  the  former,  and 
especially  the  fact  that  this  higher  elastic  limit  is  obtained  with 
only  a  slight  decrease  in  ductility.  About  3.50  per  cent,  of  nickel 
added  to  carbon  steel  will  increase  the  elastic  limit  nearly  50 
per  cent.,  while  reducing  the  ductility  only  about  15  to  20  per 
cent.  It  is  this  increase  in  elastic  limit  which  is  probably  the 
chief  reason  for  the  increased  resistance  of  nickel  steel  to  what 
is  known  as  "fatigue,"  that  is  to  say,  its  resistance  to  repeated 
stresses  and  alternating  stresses1  under  which  all  steel  will  ulti- 
mately break  down,  even  though  the  load  is  far  less  than  that 
it  can  bear  indefinitely  if  constantly  applied.  It  is  probable 
that  the  molecular  structure  of  nickel  steel  is  also  advantageous 
in  this  same  connection.  About  3.50  per  cent,  of  nickel  will 
give  steel  approximately  six  times  the  life  in  resistance  to  fatigue. 
The  records  of  shipping  show  that  the  great  majority  of  acci- 

1  Repeated  stresses  are  stresses  put  upon  a  body  at  intervals  and  relieved 
meanwhile,  while  alternate  stresses  are  stresses  first  in  compression  and  then 
in  tension,  such,  for  instance,  as  the  stresses  in  a  wire  that  is  bent  backwards 
and  forwards,  or  in  a  rotating  shaft  that  is  not  absolutely  in  alignment. 


ALLOY   STEELS  399 

dents  to  vessels  at  sea  come  from  the  breaking  of  the  propeller 
shafts  which  is  doubtless  due  to  alternate  stresses  because  these 
long  shafts  are  put  out  of  alignment  by  each  passing  wave,  and 
now  practically  all  large  vessels  use  hollow  nickel  steel  shafts. 
It  is  the  higher  elastic  limit  that  is  responsible  also  for  the  use  of 
nickel  steel  in  bridges,  ordnance,  automobile  parts,  and  wire  cables, 
for  we  may  obtain  equal  strength  with  less  weight  or  greater 
strength  with  the  same  weight.  Besides  the  elastic  limit  the  ulti- 
mate tensile  strength  of  nickel  steel  is  increased  also  by  the  addition 
of  nickel.  The  increase  is  not  so  great  in  this  particular,  and 
consequently  the  elastic  ratio,  i.e.,  the  ratio  of  the  elastic  limit 
to  the  tensile  strength,  is  increased  still  more  greatly.  The  elastic 
limit  of  ordinary  rolled  carbon  steel  should  be  at  least  one-half 
of  the  tensile  strength  while  that  of  3.50  per  cent,  nickel  steel 
should  be  at  least  60  per  cent. 

Crystalline  Structure.  —  The  crystalline  structure  of  nickel  steel 
is  more  minute  than  ordinary  carbon  steel,  and  this  is  prob- 
ably one  of  the  chief  causes  for  the  toughness  of  nickel  steel,  and 
also  for  the  fact  that  cracks  develop  in  it  relatively  slowly:  in  the 
yielding  of  steel  to  fatigue  the  damage  starts  by  the  opening  of  a 
crack  of  microscopic  proportions  through  the  cleavage  planes  of 
the  crystals,  and  this  crack  grows  and  spreads  from  crystal  to 
crystal  until  it  is  visible  to  the  unaided  eye,  after  which  it  proceeds 
with  still  greater  rapidity.  As  already  stated,  this  development 
is  much  slower  in  nickel  steel  than  in  carbon  steel.  Furthermore 
if  an  armor  plate  is  struck  by  a  projectile,  it  does  not  crack  so 
easily,  and  the  cracks  do  not  extend  so  far  if  the  plate  is  made  of 
nickel  steel.  This  fact  and  the  greater  strength  of  nickel  steel  are 
the  chief  reasons  for  the  3.25  per  cent,  of  nickel  in  all  modern 
armor  plate. 

Modulus  of  Elasticity.  —  The  modulus  of  elasticity  of  nickel 
steel  containing  not  more  than  4  or  5  per  cent,  nickel  is  about  the 
same  as  that  of  carbon  steel,  namely,  about  29,500,000  pounds 
per  square  inch.  With  higher  contents  of  nickel,  however,  and 
especially  with  more  than  20  per  cent,  of  nickel,  the  modulus 
of  elasticity  is  lower.  This  results  in  the  steel  being  much  more 
resilient  or  springy,  and  this  is  one  of  the  important  reasons  why 
not  more  than  4  per  cent,  of  nickel  is  put  into  structural  steels, 
for  a  bridge  built  of  steel  which  was  resilient,  even  though  strong, 
would  vibrate  so  much  with  the  motion  of  a  passing  load  as  to 


400  THE   METALLURGY  OF   IRON  AND   STEEL 

be  unpleasant,  and  even  unsafe  on  account  of  the  repeated  stresses 
set  up.  The  price  of  nickel,  of  course,  enters  into  the  limita- 
tion of  the  amount  used  in  structural  material  as  well,  and  it  is 
found  that  3.50  per  cent,  can  be  added  without  great  expense 
and  with  beneficial  results. 

Hardness.  —  Nickel  steel  is  considerably  harder  than  carbon 
steel,  though  not  so  much  so  but  that  it  can  be  machined  without 
difficulty.  This  is  taken  advantage  of  in  the  use  of  nickel-steel 
railroad  rails  for  curves  and  other  locations  where  the  steel  soon 
wears  out.  The  additional  strength  of  the  nickel  steel  is  also  an 
advantage  in  this  connection  and  nickel-steel  rails  have  been  tried 
with  success  upon  the  famous  horseshoe  curve  of  the  Pennsylvania 
Railroad  and  other  places.  The  hardness  of  nickel  steel  is  also 
accompanied  by  a  lower  coefficient  of  friction,  and  those  properties, 
together  with  the  additional  strength,  are  taken  advantage  of  in  the 
use  of  nickel  steel  in  axles  for  automobiles,  locomotives  and  rail- 
road cars.  Equal  strength  can  be  obtained  in  an  axle  of  smaller 
size  which  has,  of  course,  less  bearing  surface,  and  therefore  still 
further  reduced  friction. 

Soundness.  —  Nickel -steel  castings  are  relatively  free  from 
blowholes  and  this  together  with  the  strength  is  a  reason  for  the 
use  of  this  material'  for  castings.  They  also  have  a  lower  melting 
point  and  run  more  easily  in  the  molds. 

Expansibility.  —  The  coefficient  of  expansion  of  nickel  steel  is 
one  of  its  most  astonishing  and  unusual  characteristics,  for  in  dif- 
ferent samples  it  varies  all  the  way  from  practically  zero  up  to  the 
ordinary  figure  for  carbon  steels. 

Colby1  gives  the  following  figures  for  the  average  coefficient 
of  expansion  for  each  1°  C.  temperature: 

Carbon  Steel 0.00001036  (Guillaume) 

Carbon  Steel  (.25 per  cent.  C.) 0.00001150  (Charpy) 

Soft  Carbon  Steel 0.00001078  (Browne) 

5.00  per  cent.  Nickel  Steel 0.00001053  (Guillaume) 

Invar.  —  But  the  coefficient  of, expansion  with  the  ordinary 
atmospheric  changes  of  temperature  becomes  less  and  less  as  the 
percentage  of  nickel  increases  until,  when  we  reach  36  per  cent, 
of  nickel,  it  is  less  than  any  metal  or  alloy  known  and  amounts 
practically  to  zero.  This  alloy  is  patented  and  sold  under  the 

1  Page  79  of  No.  152,  page  420. 


ALLOY   STEELS  401 

name  of  "  Invar  "  and  is  used  for  scientific  instruments,  pendulums 
of  clocks,  steel  tape-measures  for  accurate  survey  work,  etc.  In  a 
paper  read  before  the  American  Association  for  the  Advancement 
of  Science  in  December,  1906,  it  was  stated  that  tapes  made  of 
invar  used  experimentally  for  United  States  Government  survey 
work  showed  a  very  great  increase  in  accuracy  over  ordinary  steel 
tapes,  and  also  in  rapidity  of  use.  These  tapes  varied  an  infini- 
tesimal amount  during  the  first  few  months,  after  which  they  be- 
came practically  constant  in  length.  The  cause  of  this  peculiar 
effect  of  nickel  upon  the  dilation  of  steel  with  an  increase  in  tem- 
perature is  a  result  of  the  effect  of  nickel  upon  the  critical  ranges  of 
the  steel,  which  we  shall  describe  later. 

Platinite.  —  As  the  amount  of  nickel  increases  beyond  36 
per  cent.,  there  is  a  slight  increase  in  the  coefficient  of  expan- 
sion so  that  when  we  reach  about  42  per  cent,  of  nickel,  the  steel 
has  the  same  coefficient  of '  expansion  and  contraction  with  the 
atmospheric  temperature  as  has  glass.  It  can  therefore  be 
used  for  the  manufacture  of  'armored  glass/  i.e.,  a  plate  of  glass 
into  which  a  network  of  steel  wire  has  been  rolled  and  which 
is  used  for  fire-proofing,  etc.,  because  even  though  the  glass  should 
break,  it  is  held  together  by  the  steel  network.  It  can  also  be 
used  for  the  electric  connections  passing  through  the  glass  plugs 
in  the  base  of  incandescent  electric  lights.  Platinum  has  been 
used  altogether  for  this  latter  purpose,  in  spite  of  its  very  high 
cost,  because  it  was  the  only  metal  hitherto  known  that  had 
the  correct  coefficient  of  expansion  and  contraction,  and  there- 
fore the  name  of  '  platinite '  has  been  given  to  this  patented  nickel- 
steel  alloy.  It  is  much  more  valuable  for  employment  in  the 
electric  light  industry  than  for  armored  glass,  because  ordinary 
steel,  although  its  coefficient  of  expansion  is  too  large,  still  suffices 
for  the  majority  of  armored  glass  work. 

Corrodibility.  —  Nickel  steel  corrodes  less  than  carbon  steel, 
both  in  the  presence  of  the  atmosphere,  fresh  and  salt  water,  the 
ordinary  acids,  the  smoke  of  locomotives,  etc.  Moreover,  the  de- 
gree of  corrodibility  decreases  with  each  increase  in  the  amount  of 
nickel  present.  For  this  reason  30  per  cent,  nickel  boiler  tubes 
have  been  used,  especially  in  marine  boilers.  The  great  expense  of 
this  material  is,  however,  an  obstacle  to  its  common  adoption. 

Other  Properties.  —  Ordinary  nickel  steel  containing  about  3.50 
per  cent,  of  nickel  has  several  other  properties  which  distinguish  it 


402  THE  METALLURGY  OF   IRON  AND   STEEL 

from  carbon  steel,  among  which  we  may  mention  its  higher  com- 
pressive  strength  and  greater  toughness  under  impact.  This 
latter  makes  nickel  steel  especially  resistant  to  shocks,  for  it  not 
only  takes  a  greater  blow  to  bend  it  but  it  will  bend  through  more 
of  an  angle  before  cracking.  Nickel  steel  also  has  a  greater  shear- 
ing strength  which  makes  it  advantageous  for  rivets,  because 
smaller  rivets  may  be  used  and  this  means  smaller  holes  in  the 
structural  members  that  are  being  joined,  and  consequently  a 
greater  area  of  these  members  left  to  support  the  strains  upon 
them.  In  this  connection,  however,  it  should  be  remembered  that 
nickel  steel  does  not  weld  as  well  as  carbon  steel,  and  therefore 
greater  care  is  required  in  upsetting  the  rivets  during  the  processes 
of  construction.  Nickel  segregates  very  little  in  iron  and  it  also 
has  the  advantageous  property  of  hindering  the  other  elements 
from  segregation,  so  that  nickel  steel  is  less  liable  to  these  irregu- 
larities than  carbon  steel.  In  steel  over  0.50  per  cent,  carbon, 
nickel  has  a  tendency  to  make  the  carbon  come  out  as  graphite. 

Critical  Changes.  —  Nickel  has  a  very  important  effect  upon  the 
critical  changes  of  iron  and  steel.  This  fact  will  readily  be  believed 
because  it  is  known  that  many  of  the  elements  added  to  steel  pro- 
duce important  changes  in  the  critical  points.  G.  B.  Waterhouse,1 
while  investigating  under  my  direction  the  effect  of  3.80  per  cent, 
of  nickel  upon  iron,,  showed  that  this  amount  of  nickel  did  .not 
make  any  appreciable  difference  in  the  mode  of  occurrence  of  the 
critical  points  on  cooling,  but  it  did  reduce  the  temperature  at 
which  these  critical  points  came  by  about  75°  C.  (167°  F.). 

As  the  amount  of  nickel  in  the  alloys  increases  the  tempera- 
tures at  which  the  critical  ranges  occur  become  lower  and  lower 
until  we  reach  25  per  cent,  of  nickel,  when  the  critical  ranges  occur 
below  the  atmospheric  temperature.  That  is  to  say,  the  steel  does 
not  ordinarily  cool  to  the  point  at  which  the  solid  solution  is  decom- 
posed and  the  beta  and  alpha  allotropic  modifications  are  assumed. 

Irreversible  Transformations.  —  The  great  peculiarity  of  the 
critical  changes  of  the  nickel-steel  alloys  with  less  than  25  per  cent, 
of  nickel  is  that  they  are  irreversible.  By  this  we  mean  that  the 
change  which  takes  place  at  one  temperature  on  cooling  is  not  re- 
versed on  heating  at  the  same  temperature,  or  anywhere  near  that 
temperature.  In  other  words  when  we  cool  a  nickel  steel  contain- 
ing 20  per  cent,  nickel  the  solid  solution  is  not  decomposed  and  the 
1  No.  150,  page  419. 


FIG.  292.  —  1.54  PER  CENT.  CARBON. 

ROLLED. 

Magnified  225  diameters. 
Etched  with  picric  acid. 


FIG.  293.  —  1.24  PER  CENT.  CARBON. 

ROLLED. 

Magnified  225  diameters. 
Etched  with  picric  acid. 


FIG.  294.  —  1.24  PER  CENT.  CARBON. 

SLOWLY  COOLED   STEEL. 

Magnified  225  diameters. 

Etched  with  picric  acid. 


FIG.  295.  —  1.24  PER  CENT.  CARBON. 

COOLED  EXTREMELY  SLOWLY. 

Magnified  265  diameters. 

Etched  with  picric  acid. 


FIG.  296.  —  1.24  PER  CENT.  CARBON.         FIG.  297.  —  0.41  PER  CENT.  CARBON 
COOLED  EXTREMELY  SLOWLY.  COOLED  EXTREMELY  SLOWLY. 

Magnified  265  diameters.  Magnified  265  diameters 

Etched  with  picric  acid.  Etched  with  picric  acid. 

Nickel  steels  containing  about  3.80  per  cent,  nickel,  0.12  per  cent,  silicon,  0.05  per  cent, 
manganese,  0.014  per  cent,  sulphur,  0.008  per  cent,  phosphorus,  0.01  per  cent,  aluminum. 
(G.  B.  Waterhouse  in  the  Author's  Laboratory.) 


404  THE  METALLURGY  OF   IRON  AND   STEEL 

alpha  allotropic  modification  is  not  assumed  until  we  get  below  100° 
C.  (212°  F.).  But  having  cooled  the  steel  to  that  point  and  decom- 
posed the  solution,  we  can  now  heat  it  nearly  to  600°  C.  (1112°  F.) 
before  the  reverse  change  takes  place  and  we  again  form  the  solid 
solution  and  the  gamma  allotropic  modification.  In  other  words, 
it  is  possible  to  have  a  sample  of  nickel  steel  between  100°  and 
600°  C.  which  shall  be  in  either  condition  we  like.  With  20  per  cent, 
of  nickel,  nearly  1  per  cent,  of  carbon  and  1.40  per  cent,  of  man- 
ganese, the  transformation  point  on  cooling  is  188°  below  zero  C. 
(306°  below  zero  F.),  while  the  transformation  point  on  heating  is 
well  above  the  atmospheric  temperature.  Therefore  at  atmos- 
pheric temperature  we  may  have  such  a  piece  of  steel  in  either 
condition  we  like,  and  a  very  interesting  experiment  is  formed 
by  having  a  bar  of  this  steel  one  end  of  which  has  been  cooled  more 
than  188°  below  zero  C.,  while  the  other  end  has  not.  The  end 
that  has  been  cooled  will  be  magnetic  and  the  other  end  non- 
magnetic. 

When  we  have  more  than  40  per  cent,  of  nickel  in  our  steels,  the 
critical  transformations  are  reversible  like  ordinary  steels.  That 
is  to  say,  they  occur  at  nearly  the  same  temperature  on  heating 
as  the  reverse  change  does  on  cooling.  It  is  an  interesting  fact 
that  the  steels  in  which  the  irreversibility  of  the  transformation  is 
most  marked,  —  that  is  to  say,  the  steels  from  12  to  25  per  cent,  of 
nickel,  —  have  the  highest  strength  and  elastic  limit;  at  about  25  to 
30  per  cent,  of  nickel,  where  the  irreversible  transformation  is  most 
erratic,  and  beyond  that  point,  the  strength  is  much  lower.  The 
whole  interesting  question  of  reversible  and  irreversible  transforma- 
tion is  discussed  very  fully  in  Dumas 's  paper  No.  153,  referred  to 
at  the  end  of  this  chapter. 

Occurrence  of  Nickel.  —  Waterhouse  tested  his  steel  contain- 
ing 3.80  per  cent,  of  nickel  and  found  that  a  part  of  the  nickel 
was  dissolved  in  the  cementite  which  had  the  formula  (FeNi)3C. 
The  amount  of  nickel  in  the  cementite  was  not,  however,  as  great  as 
that  in  the  ferrite.  That  is  to  say,  the  steel,  as  a  whole,  contained 
3.80  per  cent,  nickel,  while  the  cementite  contained  only  1.86  per 
cent.,  showing  that  the  nickel  dissolves  more  easily  in  the  ferrite 
than  it  does  in  the  cementite. 

Micro-structure.  —  In  Figs.  292  to  297  I  show  some  photomicro- 
graphs of  nickel  steels  taken  by  Waterhouse,  and  in  reference 
No.  1522  will  be  found  L.  Quillet's  researches  upon  this  subject. 


ALLOY  STEELS  405 


MANGANESE  STEEL 

We  owe  the  discovery  of  manganese  steel  to  the  untiring  in- 
genuity of  Robert  A.  Hadfield,  of  Sheffield,  England,  and  its 
story  will  be  an  inspiration  to  every  inventor,  for  it  resulted  in  a 
material  whose  properties  are  not  only  the  opposite  of  what  we 
might  reasonably  have  expected  on  logical  grounds,  but  whose 
combination  of  great  hardness  and  great  ductility-  was  hitherto 
unknown  and  might  readily  have  been  believed  to  be  impossible. 
Constant  study  and  perseverance  must  have  been  the  qualities 
that  led  to  this  revolutionary  invention,  and  it  has  established 
beyond  question  the  principle  that  because  a  given  amount  of  any 
element  produces  a  given  effect  upon  steels,  it  does  not  follow  that 
a  different  amount  will  give  the  same  effect  in  a  different  degree. 
Indeed  a  different  amount  may  give  an  entirely  different,  and  per- 
haps an  exactly  contrary,  effect,  as  is  the  case  of  the  effect  of  man- 
ganese upon  steel. 

When  the  manganese  in  steel  is  over  1  per  cent,  the  metal 
becomes  hard  and  somewhat  brittle,  and  these  qualities  increase  in 
intensity  with  every  increase  of  manganese  until,  when  we  have 
4  to  5.50  per  cent,  the  steel  can  be  powdered  under  the  hammer. 
But  as  the  manganese  is  increased  from  this  point,  these  properties 
do  not  increase  and  when  we  reach  7  per  cent.,  an  entirely  new 
set  of  properties  begin  to  appear.  These  are  well  marked  at  10" 
per  cent,  of  manganese,  and  reach  a  maximum  at  12  to  15  per  cent. 

Composition.  —  Manganese  steel  usually  contains  about  12  to  13 
per  cent,  of  manganese  and  1 .25  to  2  per  cent,  of  carbon.  With  this 
amount  of  manganese  the  strength  and  ductility  of  the  material 
reaches  its  maximum.  This  high  carbon  has  been  necessary  hither- 
to, because  ferro-manganese  contains  much  carbon,  which  therefore 
unavoidably  finds  its  way  into  the  steel.  In  recent  years,  however, 
manganese  metal,  relatively  free  from  carbon,  has  been  made  by 
the  Goldschmidt  Thermit  process  and  otherwise,  and  this  enables 
manganese  steel  low  in  carbon  to  be  made,  which  is  now  in  process 
of  development  and  is  giving  evidence  of  having  new  and  useful 
properties  of  its  own  and  of  being  more  easily  treated  and  worked. 

Treatment.  —  After  manganese  steel  has  been  cast  into  an  ingot 
or  casting,  and  slowly  cooled,  it  is  almost  as  brittle  as  glass.  But 
it  is  then  reheated  to  a  temperature  of  more  than  1000°  C.  (1832° 


406  THE  METALLURGY  OF   IRON  AND  STEEL 

F.)  and  rapidly  cooled  by  plunging  it  into  water.  The  tempera- 
ture from  which  it  is  necessary  to  quench  it  can  readily  be  deter- 
mined, for  it  must  be  so  high  that  when  the  steel  is  quenched  little 
blue  flames  of  hydrogen  will  appear  on  the  surface  of  the  water. 
These  are  due  to  the  decomposition  of  water  into  hydrogen  and 
oxygen  by  the  intense  heat  of  the  steel  at  the  moment  of  touching 
it.  The  steel  which  was  very  brittle  before  this  treatment  is  after- 
wards as  ductile  as  soft  carbon  steel  or  wrought  iron,  while  its 
tensile  strength  is  about  three  times  as  great.  Thus  the  sudden 
cooling,  which  produces  brittleness  in  ordinary  steel,  produces 
ductility  in  manganese  steel.  The  hardness  of  the  manganese 
steel  is  about  the  same  in  the  slowly  cooled  and  in  the  quenched 
condition,  and  is  so  great  that  it  is  not  commercially  practicable 
to  machine  it  and  there  is  no  method  known  of  making  it  softer. 

Manganese  steel  must  be  heated  very  slowly  and  uniformly 
lest  it  crack.  It  is  also  very  difficult  to  forge  it,  and  this  can  only 
be  accomplished  within  a  narrow  range  of  temperature  above  a 
red  heat  and  by  beginning  with  very  light  taps  of  the  hammer. 
After  a  little  working  it  becomes  so  tough  that  it  can  be  rolled, 
although  somewhat  gingerly.  The  knowledge  as  to  the  proper 
method  of  performing  these  manipulations  is  only  in  a  few  hands, 
and  it  is  only  recently  that  any  large  amount  of  forging  has  been 
possible.  Even  railroad  rails  for  curves  have  generally  been  made 
by  casting  the  metal  in  a  mold  of  the  proper  shape,  including  the 
curvature,  and  this  has,  of  course,  involved  a  great  deal  of  expense. 

Uses.  —  Manganese  steel  is  used  chiefly  for  the  jaws  and 
wearing  parts  of  rock-crushing  machinery  and  similar  apparatus, 
for  railroad  frogs  and  crossings,  for  railroad  rails  on  curves,  mine 
car  wheels,  and  burglar-proof  safes.  Its  life  in  these  classes  of  serv- 
ice is  very  many  times  that  of  all  other  kinds  of  steel,  because  it 
is  not  only  extremely  hard  but  is  without  brittleness.  There  is  a 
famous  curve  on  the  Boston  elevated  railroad  where  carbon-steel 
rails  were  worn  out  in  a  very  short  time  and  the  use  of  manganese- 
steel  rails  has  proved  very  advantageous  and  economical.  The 
use  of  the  steel  for  burglar-proof  safes  is  also  very  advantageous, 
because  there  is  no  known  method  of  making  the  steel  soft  enough 
to  be  penetrated  by  a  drill.  The  uses  of  manganese  steel  are  limited 
chiefly  because  the  metal  must  ordinarily  be  formed  by  casting, 
since  machining  and  cutting  to  shape  is  practically  out  of  the 
question,  and  forging  is  difficult.  For  structural  work  the  advan- 


ALLOY   STEELS  407 

tages  of  its  high  combination  of  strength  and  ductility  are  some- 
what offset  by  its  low  elastic  limit,  which  is  only  about  35  per  cent, 
of  its  ultimate  tensile  strength.  One  peculiarity  of  manganese  steel 
is  that  when  it  yields  to  tensile  stresses  it  is  elongated  more  uniform- 
ly over  its  whole  length  than  carbon  steel,  which  suffers  its  greatest 
elongation  near  the  point  of  final  rupture  where  a  certain  amount 
of  "necking"  takes  place.  It  will  be  remembered  that  on  page 
65  we  showed  that  wrought  iron  stretched  more  uniformly  over 
its  whole  length  than  steel;  manganese  steel  has  this  property  in  a 
still  more  marked  degree  even  than  wrought  iron. 

Critical  Changes.  —  The  hardness  of  manganese  steel  is  due, 
in  part,  to  the  hardness  of  manganese,  but  still  more  potently  to 
the  fact  that  the  steel  is  in  the  austenitic  condition.  That  is  to 
say  the  manganese  has  reduced  the  temperature  at  which  the 
critical  changes  occur  below  that  of  the  atmosphere,  and  there- 
fore manganese  steel  consists  entirely  of  austenite.  It  is,  of  course, 
non-magnetic.  Whether  or  not  it  is  capable  of  irreversible  trans- 
formation like  nickel  steel  is  not  known,  for  its  nature  and 
manufacture  is  kept  as  secret  as  possible  by  those  who  know  it, 
for  trade  reasons. 


CHROME  STEEL 

Chromium  has  the  effect  of  making  the  critical  changes  of  steel 
take  place  much  more  slowly.  Therefore  chromium  steels  are 
capable  of  greater  hardness,  because  rapid  cooling  is  able  more 
completely  to  prevent  the  decomposition  of  austenite.  They 
contain  usually  1  to  2  per  cent,  of  chromium  and  from  0.80  to  2  per 
cent,  of  carbon  and  are  used  in  the  hardened  state.  They  are  par- 
ticularly adapted  for  making  armor-piercing  projectiles,  on  account 
of  their  hardness  and  also  their  very  high  elastic  limit.  They  are 
also  used  for  armor  plate  for  the  same  reason,  for  parts  of  crushing 
machinery,  and  for  very  hard  steel  plate.  This  latter  is  not  or- 
dinarily used  by  itself,  but  is  made  into  3-ply  and  5-ply  plate  for 
plows  and  burglar-proof  safes,  as  described  on  page  195,  for  if  the 
hardened  chrome  steel  were  used  alone,  its  brittleness  would 
cause  it  to  be  shattered. 

Armor  Plate.  —  Krupp  armor  plate  contains  about  3.25  per 
cent,  of  nickel,  1.50  per  cent,  of  chromium  and  0.25  per  cent,  of 
carbon.  Its  further  manufacture  is  described  on  page  228. 


408  THE  METALLURGY   OF   IRON  AND   STEEL 

Automobile  Steels.  —  Chromium  up  to  about  2  per  cent,  is  also 
used  for  automobile  steels  where  hardness  is  required,  as  for  in- 
stance in  gears  and  other  parts  requiring  great  hardness  or  great 
strength.  For  the  latter  purpose  it  is  more  common  to  use  a  nickel- 
chrome  steel,  and  this  is  often  subjected  to  a  double  heat  treatment 
or  a  simple  oil  tempering.  This  treatment  has  the  effect  of  greatly 
increasing  its  strength  and  elastic  limit,  so  that  steels  of  this  char- 
acter will  have  properties  similar  to  those  shown  in  Table  XXX. 
There  cannot  be  said  to  be  any  uniform  composition  or  method  of 
treatment  for  automobile  steels,  and  my  inquiries  among  American 
manufacturers  seem  to  indicate  that  there  is  not  very  much  of  the 
high-priced  alloy  steels  used  in  American  cars,  except  for  the 
frames  which,  as  already  stated,  are  frequently  made  of  3.50  per 
cent,  nickel  steel.  The  next  most  important  use  is  probably  for 
gears  of  chrome  steel  of  nickel-chrome  steel,  first  case-hardened  by 
cementing  with  carbon  to  a  depth  of  an  eighth  of  an  inch  or  so,  and 
then  heat-treated.  The  composition  and  treatment  of  alloy  steels 
used  in  French  automobiles  is  shown  more  fully  in  Quillet's  article, 
No.  1514. 

SELF-HARDENING  AND  HIGH-SPEED  TOOL  STEELS 

Self -hardening  Steel.  —  Self -hardening  steel  is  steel  which  is 
hard  without  being  subjected  to  any  heat  treatment  or  other 
process  for  making  it  so.  It  is  steel  which  cannot  be  made  soft,  or 
annealed,  by  any  process  known  at  present.  It  is  often  called  '  air- 
hardening  steel '  because  when  it  cools  in  the  air  from  a  red  heat 
or  above,  it  is  not  soft  like  ordinary  steel,  but  is  hard  and  capable 
of  cutting  other  metals.  Manganese  steel  is  a  typical  self-harden- 
ing steel  and  so  obviously  is  any  steel  which  is  in  the  austenitic 
condition  at  atmospheric  temperatures,  —  that  is  to  say,  whose 
critical  temperature  is  below  the  atmospheric  temperature.  All 
the  self-hardening  steels  are  therefore  non-magnetic. 

Mushet  Steel.  —  The  name  'self-hardening'  steel  was  first 
applied  to  an  alloy  steel  invented  by  Robert  Mushet  and  which 
owed  its  self-hardening  properties  to  the  simultaneous  presence 
of  both  tungsten  and  manganese.  The  analyses  varied  greatly 
but  were  probably  limited  to  between  4  and  12  per  cent,  of  tungsten 
with  2  to  4  per  cent,  of  manganese  and  1.50  to  2.50  per  cent,  of 
carbon.  A  typical  sample  and  one  having  excellent  qualities 


ALLOY   STEELS  409 

contained  about  9  per  cent,  of  tungsten,  2.50  per  cent,  of  manganese, 
and  1.85  per  cent,  of  carbon.  This  steel  is  incapable  of  being 
made  soft  by  any  known  process  and  is  non-magnetic.  It  is 
one  of  those  curious  phenomena  met  with  in  the  metallurgy  of 
steel,  where  a  combination  of  two  elements  will  produce  a  result 
entirely  different  from  anything  that  might  be  predicated:  Tung- 
sten does  not  lower  the  temperature  of  the  critical  change  in  steel 
and  2.50  per  cent,  of  manganese  has  but  a  slight  effect  in  that  direc- 
tion. Nevertheless  the  combination  of  these  two  reduces  the 
critical  point  below  the  atmospheric  temperature. 

Mushet  steel  has  been,  for  many  years,  a  famous  tool  steel  be- 
cause of  its  capacity  for  performing  a  large  amount  of  heavy  cutting 
work.  It  is  very  hard  and  durable  and  will  retain  its  cutting  edge 
for  a  long  time  and  under  very  severe  service.  It,  or  its  equivalent, 
is  used  very  largely  at  the  present  time  for  very  heavy,  or  deep,  cuts 
and  especially  for  cutting  extra -hard  metal,  such  as  the  roughing 
cuts  on  armor  plate  and  other  hard  alloys.  The  cutting  speed  of 
which  it  is  capable  is  not  much,  if  any,  greater  than  ordinary 
carbon  tool  steel,  but  the  economy  of  its  use  is  due  to  the  fact 
that  it  will  take  such  deep  cuts  and  last  so  long  without  regrinding. 

Other  Self -hardening  Tool  Steels.  —  The  2.50  per  cent,  of  man- 
ganese in  Mushet  steel  can  be  replaced  by  1  or  2  per  cent,  of 
chromium  and  again  produce  a  self-hardening  tool  steel  which 
has  the  advantageous  properties  of  Mushet  steel.  This  result  is 
even  more  astonishing  than  the  self-hardening  properties  of 
Mushet  steel,  because  chromium  has  a  tendency  to  raise  the 
temperature  at  which  the  critical  change  comes,  and  yet  the 
addition  of  1  or  2  per  cent,  of  chromium  to  a  tungsten  steel,  which 
was  not  previously  self-hardening  and  whose  critical  temperature 
was  about  600°  C.  (1112°  F.),  reduces  the  critical  temperature 
to  below  the  atmosphere.  We  may  also  replace  the  9  per  cent, 
of  tungsten  in  Mushet  steel  with  4  to  6  per  cent,  of  molybdenum, 
and  it  is  stated  that  this  latter  change  produces  a  self-hardening 
tool  steel  which  is  a  little  tougher  than  Mushet  steel. 

Taylor  and  White.  —  Frederick  W.  Taylor  and  Maunsel  White 
of  the  Bethlehem  Steel  Works  experimented  for  a  long  period 
of  time  with  the  self-hardening  steels  existing  in  1899  and  previ- 
ously, for  the  purpose  of  improving  them  by  heat  treatment.  The 
full  record  of  these  and  other  researches  were  presented  by  Taylor 
in  his  presidential  address  to  the  American  Society  of  Mechanical 


410  THE  METALLURGY  OF   IRON  AND   STEEL 

Engineers  in  1906,  and  form  one  of  the  most  interesting  records 
of  the  kind  ever  presented  to  the  world.  The  result  of  these 
experiments  was  to  produce  a  wholly  new  kind  of  steel  which 
has  fairly  revolutionized  the  machine  shop  industry  of  the  world. 
Taylor  and  White  found  that  by  applying  a  new  method  of  heat 
treatment  to  the  self-hardening  tool  steels,  they  gave  them  much 
greater  toughness  at  a  red  heat,  so  that  they  could  do  their  cut- 
ting work  at  a  speed  so  fast  that  the  point  of  the  tool  would  be- 
come red  hot  with  the  heat  of  friction  and  the  great  chips  of  steel, 
which  were  thick  and  heavy  on  account  of  the  depth  of  cut  which 
could  be  made,  were  raised  to  a  temperature  of  nearly  300°  C.  (572° 
F.).  In  other  words,  the  steel  tool  never  lost  its  temper  nor  its 
toughness  at  a  red  heat.  The  heat  treatment  which  Taylor  and 
White  employed  consisted  in  raising  the  steel  almost  to  the  melting 
point  and  then  plunging  it  in  a  bath  of  molten  lead  at  a  temperature 
between  700° and  850° C.  (1300°  and  1550°  F.),  where  it  was  kept 
until  it  was  of  the  same  temperature  as  the  bath,  and  then  re- 
moved and  cooled  by  plunging  into  oil.  They  usually  followed 
this  cooling  by  reheating  the  steel  to  a  temperature  between  370° 
and  670°  C.  (700°  and  1240°  F.). 

The  first  public  exhibition  of  the  Taylor  and  White  steel  was 
made  at  the  Paris  Exposition  in  1900  and  created  first  incredulity 
and  then  astonishment.  The  amount  of  work  performed  by  a  tool 
was  unheard  of,  as  also  was  the  speed  at  which  the  tool  was  made 
to  travel  through  the  metal  it  was  cutting,  and  the  length  of  time 
that  elapsed  before  it  was  necessary  to  regrind  it.  It  was  realized 
that  a  new  epoch  in  the  tool-steel  industry  had  been  inaugurated. 
The  fact  that  the  method  of  heat  treatment  used  by  Taylor  and 
White  was  subsequently  shown  to  be  unnecessary  and  that  there- 
fore the  manufacture  of  high-speed  steel  tools,  having  qualities 
like  theirs,  was  begun  by  everybody,  in  no  way  lessens  the  credit 
due  them  for  teaching  the  world  how  to  produce  a  new  kind  of 
metal  and  effecting  a  tremendous  decrease  in  the  price  of  machine 
work. 

High-speed  Steels.  —  The  name  'high-speed  steels'  was  not 
given  by  Taylor  and  White  to  their  product,  but  has  subsequently 
been  adopted  for  all  steels  capable  of  these  rapid-cutting  speeds 
which  theirs  had.  Soon  after  they  had  shown  the  world  what  could 
be  done,  it  was  found  that  the  only  heat  treatment  necessary  to 
give  the  steel  its  peculiar  hardness  and  toughness  at  a  low  red  heat 


ALLOY  STEELS  411 

was  to  raise  it  to  a  temperature  very  near  its  melting  point  and 
then  cool  it  witn  moderate  rapidity,  as  for  example  by  holding  it 
in  a  blast  of  cold  air  until  it  was  below  a  red  heat.  The  essential 
feature  seems  to  be  that  the  steel  shall  attain  a  high  temperature 
which,  in  many  cases,  is  so  great  that  melted  oxide  drops  from  it, 
and  it  is  almost  ready  to  scintillate,  —  that  is  to  say,  it  has  almost 
crossed  the  line  Aa  in  Fig.  246,  page  314.  After  this  heating  it 
sometimes  suffices  to  merely  allow  the  steel  to  cool  in  air,  but  in 
this  case  its  hardness  is  not  as  great,  and  cooling  in  a  stream  of  air 
is  more  usual. 

Composition.  —  It  was  also  soon  found  that  the  composition 
of  the  self-hardening  steels  was  not  the  best  one  for  high-speed 
steels.  Tungsten  was  the  element  which  gave  the  steel  the  prop- 
erties of  hardness  and  toughness  at  a  red  heat.  After  the  peculiar 
heat  treatment  had  been  learned  and  the  presence  of  manganese 
or  chromium  in  addition  to  the  tungsten  was  shown  to  be  unneces- 
sary, it  was  found  that  more  durable  qualities  could  be  obtained  by 
increasing  the  percentage  of  tungsten,  and  steels  have  been  put 
upon  the  market  with  even  as  high  as  24  per  cent,  of  this  element. 
At  the  same  time  the  carbon  was  greatly  reduced  and  at  the 
present  usually  varies  from  0.40  to  0.80  per  cent,  in  the  best  high- 
speed steels.1 

It  was  also  found  that  molybdenum  could  replace  tungsten 
as  far  as  producing  high-speed  qualities  was  concerned,  and  man}7 
believe  that  the  molybdenum  steels  are  more  tough  and  durable 
than  the  tungsten  steels.  Some  difficulty  was  met  with  at  first  in 
working  the  molybdenum  steels  as  they  proved  to  be  seamy  ard 
liable  to  cracks,  but  this  was  overcome  with  experience.  The 
molybdenum  steels  do  not  require  so  high  a  temperature  for  heating 
previous  to  cooling  down  in  the  air  blast  as  the  tungsten  steels. 

1  It  is  commonly  stated  in  the  trade  that  tungsten  will  take  the  place  of 
carbon  in  producing  hardness,  but  this  is  not  true.  It  is  far  more  correct  to 
say  that  tungsten  will  assist  carbon  in  producing  hardness  and  therefore  with 
high  tungsten  steels  we  may  have  lower  carbon.  This  distinction  may  appear 
merely  academic,  but  it  is  well  worth  recognition  by  those  who  expect  to  make 
a  study  of  these  steels.  No  amount  of  tungsten  or  any  other  element  will  make 
steel  hard  in  the  absence  of  carbon,  or  even  when  the  carbon  is  low.  The  tung- 
sten produces  hardness  by  its  effect  upon  the  condition  of  the  carbon,  —  that  is 
by  helping  to  retain  the  carbon  in  its  solid  solution,  —  and  not  by  any  effect  of 
its  own.  It  is  for  this  reason  that  a  lesser  amount  of  carbon  will  produce 
hardness  in  the  presence  of  tungsten  or  some  similar  agent. 


412  THE  METALLURGY  OF   IRON  AND  STEEL 

According  to  the  researches  of  Carpenter,1  the  molybdenum 
steels  should  be  heated  between  1000°  arid  1100°  C.  (1832°  and 
2012°  F.),  while  the  tungsten  steels  must  be  heated  in  the  neigh- 
borhood of  1200°  C.  (2192°  F.).  Furthermore  it  only  takes  about 
one-half  as  much  molybdenum  as  tungsten  to  produce  the  desired 
result,  which  means  that  there  is  more  iron  in  the  molybdenum 
steels  than  in  the  tungsten  steels.  In  other  respects  the  analysis 
of  the  molybdenum  and  the  tungsten  steels  is  about  the  same, 
containing  usually  0.60  to  0.80  per  cent,  of  carbon  and  anywhere 
from  zero  chromium  up  to  sometimes  as  much  as  4  per  cent. 
Indeed  chromium  is  sometimes  recommended  as  high  as  6  per 
cent,  and  over,  because  it  gives  hardness,  but  it  also  reduces 
toughness.  The  more  durable  qualities  of  the  molybdenum  steels 
than  the  tungsten  steels  are  believed  to  be  due  to  the  .larger 
amount  of  iron  in  them  and  the  lower  temperature  necessary  for 
tempering  them. 

In  some  cases  molybdenum  and  tungsten  have  been  used  to- 
gether in  high-speed  steels.  In  fact  there  are  at  the  present  time 
scores  of  brands  and  analyses  of  high-speed  steels  on  the  market, 
made  both  in  America,  England,  and  Europe  and  the  art  of  manu- 
facturing them  is  constantly  advancing  so  that  no  very  general 
results  can  be  quoted.  In  America  the  most  advantageous  per- 
centages of  molybdenum,  6  to  15  per  cent.,  are  patented  and  al- 
though at  one  time  a  great  many  tons  of  this  kind  of  high-speed 
steel  were  manufactured  and  gave  very  good  results  (containing 
usually  about  10  per  cent,  of  molybdenum)  it  can  now  be  made 
only  by  one  company,  so  that  tungsten  steels  are  more  common. 

Forging.  —  High-speed  steels  can  only  be  forged  at  tempera- 
tures above  a  bright  red  heat,  that  is  to  say  from  1050°  to  1150°  C. 
(1922°  to  2100°  F.)  and  higher. 

Annealing.  —  The  heating  and  annealing  of  high-speed  steels 
requires  a  great  deal  of  care.  They  must  be  heated  up  to  the  an- 
nealing temperature  (say  about  800°  C.  =  1472°  F.)  with  extreme 
slowness,  and  cooled  down  in  lime  or  ashes  or  in  the  furnace.  They 
are  then  soft  enough  to  be  machined  easily,  but  not  as  soft  as  car- 
bon steel. 

Tempering.  —  The  reason  tungsten  and  molybdenum  produce 
in  steel  the  high-speed  quality  of  not  losing  its  temper  at  a  red  heat 
is  because  of  their  effect  upon  the  critical  temperatures.  Their 

1  See  page  460  of  No.  1517,  page  421. 


ALLOY  STEELS  413 

effect  seems  to  be  to  prolong  the  critical  range  of  temperatures  of 
the  steel  on  slow  cooling;  that  is  to  say,  instead  of  the  critical  range 
coming  in  the  neighborhood  of  690°  C.  (1285°  F.),  as  with  the 
carbon  steels,  it  begins,  when  the  cooling  is  slow,  at  about  700°  C. 
and  spreads  out  all  the  way  down  to  300° or  400°  C.  (572°  or  752°  F.), 
or  even  lower.  Molybdenum  is  more  active  than  tungsten  in 
causing  this  prolongation  of  the  critical  range.  But  if  the  steels 
are  first  heated  to  a  very  high  temperature  (1000°  to  1100°  C.  for 
molybdenum  steel  and  1200°  C.  for  tungsten  =  1832°  to  2012°  and 
2192°  F.  respectively)  and  then  cooled  moderately  fast,  this  treat- 
ment suffices  to  prevent  the  critical  changes  altogether  and  pre- 
serves the  steel  in  the  austenitic  condition.  We  know  that  this 
austenitic  condition  is  one  of  hardness  and  toughness  and  its 
peculiarity  under  these  circumstances  is  that  it  is  not  transformed 
into  the  pearlitic  condition  until  the  steels  are  heated  to  650°  C. 
(1202°  F.)  or  thereabouts. 

Magnetic  Steels.  —  Strictly  speaking,  the  steels  used  for  per- 
manent magnets  are  not  high-speed  steels,  because,  of  course,  they 
are  never  used  for  cutting  work,  but  as  their  composition  is  so 
similar  it  seems  well  to  introduce  them  here.  A  permanent  magnet 
is  made  by  putting  a  piece  of  hardened  steel  in  a  magnetic  field  for 
a  few  moments,  as,  for  instance,  by  winding  an  insulated  wire 
around  it  and  passing  an  electric  current  through.  The  magnetic 
force  which  it  obtains  in  this  way  will  remain  in  it  for  a  very  long 
period  of  time.  It  is  found  that  a  steel  containing  about  4  to  5 
per  cent,  of  tungsten  and  0.50  to  0.70  per  cent,  of  carbon,  if  heated 
to  a  red  heat  (say  800°  C.  =  1472°  F.)  and  quenched  in  water, 
will  retain  its  magnetism  better  than  ordinary  hardened  carbon 
steel.  Sometimes  about  0.50  per  cent,  of  chromium  is  added  to 
the  alloy  also. 

SILICON  STEELS 

The  genius  of  Hadfield  has  also  given  us  a  silicon  steel  alloy 
of  importance  and  usefulness.  In  1888 1  Hadfield  investigated 
many  alloys  of  iron  and  silicon  and  although  these  showed  some 
remarkable  properties,  especially  in  the  matter  of  tempering  and 
cutting  qualities,  they  did  not  lead  to  any  alloy  steels  that  were 
produced  in  abundance.  At  a  later  period,  however,2  Hadfield 

1  See  No.  157,  page,  420.         2  U.  S.  Patent  12,691.     September  3,  1907. 


414  THE  METALLURGY  OF   IRON  AND   STEEL 

developed  a  silicon  steel  which,  after  a  double-heat  treatment, 
showed  some  truly  remarkable  magnetic  qualities.  It  had  always 
been  believed  that  pure  iron  had  the  highest  magnetic  force  and 
permeability  of  any  known  substance  or  of  any  combination  that 
could  be  produced,  but  Hadfield's  new  silicon  steel,  whose  com- 
position and  treatment  is  shown  below,  had  not  only  a  greater 
magnetic  permeability  than  the  purest  iron  but  also,  charac- 
teristic of  silicon  steels,  it  had  a  high  electrical  resistance.  Its 
hysteresis  is,  of  course,  low,  this  property  always  accompanying  a 
high  permeability.  It  is  therefore  a  very  valuable  material  for  use 
in  electromagnets,  and  in  electrical  generating  machinery  is  the 
most  efficient  material  known.  Its  high  magnetic  permeability 
gives  high  motor  efficiency,  and  in  addition  its  high  electrical 
resistance  reduces  the  "eddy  currents"  which  are  a  source  of 
waste. 

Composition  and  Treatment.  —  Hadfield's  patent  covers  silicon 
from  1  to  5  per  cent.,  but  the  alloy  which  he  recommends  con- 
tains 2.75  per  cent,  of  silicon  and  the  smallest  possible  amounts  of 
carbon,  manganese,  and  other  impurities.  Before  the  steel  is  ready 
for  use,  it  is  subjected  to  a  double-heat  treatment  by  first  heating  it 
to  between  900°  and  1100°  C.  (1652°  and  2012°  F.)  and  cooling 
quickly,  and  then  reheating  to  between  700°  and  850°  C.  (1292°  and 
1562°  F.)  and  allowing  to  cool  very  slowly.  In  some  cases  his 
second  cooling  has  been  extended  over  several  days.  He  finds  the 
best  results  by  heating  first  to  1070°  C.  (1958°  F.)  and  cooling 
quickly  to  atmospheric  temperature  and  then  heating  to  750°  C. 
(1382°  F.)  and  cooling  slowly,  after  which  he  sometimes  again 
reheats  to  800°  C.  (1472°  F.)  and  then  cools  slowly. 


VANADIUM  STEELS 

Vanadium  steels  are  still  in  their  infancy,  for  although  the 
element  has  been  used  in  steel  metallurgy  for  many  years,  it  is  only 
recently  that  any  important  development  work  has  been  carried 
on.  The  results,  however,  are  so  very  encouraging  that  we  may 
expect  great  extension  of  their  employment  and  important  progress 
in  their  metallurgy.  With  the  single  exception  of  carbon  no  ele- 
ment has  such  a  powerful  effect  upon  steel  as  vanadium,  for  it  is 
only  necessary  to  use  from  0.10  to  0.15  per  cent,  in  order  to  ob- 


ALLOY   STEELS  415 

tain  very  powerful  results,  while  0.30  per  cent,  should  probably 
not  be  exceeded  so  far  as  present  knowledge  indicates.  In  addi- 
tion to  acting  as  a  very  great  strengthener  of  steel,  especially 
against  dynamic  strains,  vanadium  also  serves  as  a  scavenger  in 
getting  rid  of  oxygen  and  possibly  nitrogen.  It  is  also  said  to 
decrease  segregation,  which  we  may  readily  believe,  as  most  of 
the  elements  which  quiet  the  steel  have  this  effect.  Vanadium 
steel  also  has  the  advantage  of  welding  readily. 

The  effect  of  vanadium  is  shown  very  well  by  Tables  XXX  and 
XXXII,1  and  it  will  be  seen  how  efficiently  this  material  resists  al- 
ternating stresses  and  the  other  forces  producing  fatigue.  It  is  to  be 
observed  that  vanadium  is  especially  advantageous  when  added  to 
nickel  and  to  chromium  steels,  greatly  increasing  their  strength, 
toughness,  and  temper.  In  this  connection  it  is  important  to  note 
that  the  nickel-vanadium  steels  have  better  quality  when  the  car- 
bon is  low,  especially  if  they  are  to  be  subjected  to  heat  treat- 
ment. 

It  would  seem  that  vanadium  should  have  especial  advantage 
in  high-speed  tool  steels,  but,  strange  to  say,  the  results  have  not 
always  been  favorable.  Nevertheless  experiments  in  this  direction 
continue. 

Manufacture.  —  Pure  vanadium  has  a  very  high  melting  point 
and  the  element  is  therefore  added  to  steel  in  the  form  of  ferro- 
vanadium.  This  alloy  should  be  added  to  the  bath  about  two  or 
three  minutes  after  the  manganese  used  for  recarburizing;  because 
if  the  vanadium  is  added  before  the  manganese,  it  is  wasted  by 
oxidation.  It  therefore  should  be  added  always  under  reducing 
conditions.  Beyond  this  there  is  no  special  difficulty  in  manu- 
facture, as  the  amount  of  alloy  used  is  so  small  and  as  it  distributes 
itself  readily  through  the  metal  and  does  not  segregate. 

Treatment.  —  Vanadium  steels  must  be  heated  gradually  but 
are  forged  without  difficulty  although  they  must  be  worked  a  little 
tenderly  at  first.  Like  all  steels,  they  must  not  be  forged  at  too 
high  a  temperature,  and  like  all  alloy  steels,  they  become  even  more 
brittle  when  forged  below  a  black  heat  than  carbon  steel  does. 

Uses.  —  It  is  advantageous  to  use  vanadium  steel  for  prac- 
tically every  purpose  that  will  stand  the  additional  price,  which  is 
about  the  same  as  that  of  3.50  per  cent,  nickel  steel.  It  is,  of  course, 
especially  useful  for  all  purposes  where  strength  and  lightness  are 
1  For  which  I  am  indebted  to  the  American  Vanadium  Co. 


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ALLOY   STEELS  419 

desired,  such  as  springs,  axles,  frames  and  other  parts  of  railroad 
rolling  stock  and  automobiles.  It  would  also  seem  to  have  special 
advantages  for  shafts  and  other  rotating  parts.  It  also  does  very 
well  for  case-hardened  gears,  on  account  of  the  good  combination 
of  hardness  and  toughness  and  has  been  used  to  some  extent  for 
steel  castings  where  resistance  to  vibration  has  been  demanded. 

Vanadium  has  also  been  added  to  cast  iron  011  account  of  its 
ability  to  remove  oxygen  and  possibly  nitrogen  (if  any  is  ever 
present),  and  because  it  makes  the  metal  more  fluid  and  tougher. 
It  is  said  also  to  make  chilled  cast-iron  rolls  more  durable  and  more 
ductile. 

TITANIUM  STEELS 

Titanium  has  not  been  used  much  for  making  alloy  steels,  but 
it  has  one  advantage  which  has  caused  its  use  to  be  recommended, 
namely,  its  high  affinity  for  nitrogen.  There  is  no  element  whose 
addition  to  iron  or  steel  would  be  expected  to  have  a  greater  effect 
in  ridding  it  of  nitrogen,  but  beyond  these  logical  arguments  the 
experiments  so  far  made  are  not  absolutely  conclusive,  although 
they  are  sufficient  to  cause  a  great  deal  of  interest  to  be  taken  in 
this  subject. 

titanium  has  often  been  found  in  pig  iron  in  very  small  quan- 
tities, but  its  presence  in  the  blast  furnace  is  usually  objected  to, 
because  it  causes  the  slags  to  be  so  infusible  and  sticky.  Ferro- 
titanium  is  now  being  made  in  electric  furnaces  where  the  tem- 
perature available  overcomes  the  difficulty  of  infusible  slags.  This 
alloy  is  added  to  iron  castings  in  amounts  such  that  the  proportion 
of  titanium  in  the  metal  will  not  exceed  0.10  to  OJ^per  cent. 
This  results  in  an  increase  in  strength  of  the  iron  of  nearly  20  to  40 
per  cent,  and  also  of  greater  hardness  and  durability  against  wear. 


REFERENCES    ON   ALLOY   STEELS 

1 50.  G.  B.  Waterhouse.     "  The  Influence  of  Nickel  and  Carbon  on 

Iron.;'  Journal  of  the  Iron  and  Steel  Institute,  vol.  ii, 
1905.  pages  376-407.  This  includes  a  bibliography  of  a 
part  of  the  subject. 

151.  G.  B.  Waterhouse.     "The  Burning,  Overheating,  and  Re- 

storing of  Nickel  Steel."     Proceedings  of  the  American 


420  THE  METALLURGY   OF   IRON   AND  STEEL 

Society  for  Testing  Materials,  vol.  vi,  1906,  pages  247- 
258. 

152.  A.  L.  Colby.     "  A  Comparison  of  Certain  Physical  Properties 

of  Nickel  Steel  and  Carbon  Steel."  Published  by  the 
Bethlehem  Steel  Company,  1903.  A  very  complete  com- 
pilation. 

153.  L.  Dumas.     "The  Reversible  and  Irreversible  Transforma- 

tions of  Nickel  Steel."  Journal  of  the  Iron  and  Steel  In- 
stitute, No.  11, 1905,  pages  255-300. 

154.  D.  H.  Browne.     "Nickel  Steel;  A  Synopsis  of  Experiment 

and  Opinion."  Transactions  of  the  American  Institute  of 
Mining  Engineers,  vol.  xxix,  1899,  pages  569-648.  Very 
complete,  with  a  good  bibliography. 

155.  R.  A.  Hadfield.     "Alloys  of  Iron  and  Manganese."     Pro- 

ceedings of  the  Institution  of  Civil  Engineers  (England), 
.       1888. 

156.  R.  A.  Hadfield.     "Manganese  Steel."     Journal  of  the  Iron 

and  Steel  Institute,  1888. 

157.  R.  A.  Hadfield.     "  Alloys  of  Iron  and  Silicon."      Ibid.,  1889. 

158.  R.  A.  Hadfield.     "Alloys  of  Iron  and  Aluminum."     Ibid., 

1890. 

159.  R.  A.  Hadfield.    "Alloys  of  Iron  and  Chromium."    Ibid., 

1892. 

1510.  R.  A.  Hadfield.     "Alloys  of  Iron  and  Nickel."    Proceedings 

of  the  Institution  of  Civil  Engineers  (England),  1899. 

1511.  R.  A.  Hadfield.     "Alloys  of  Iron  and  Tungsten."     Journal 

of  the  Iron  and  Steel  Institute,  No.  11, 1903. 

1512.  Henry  M.  Howe.     "Manganese  Steel."     Proceedings  of  the 

American  Society  of  Mechanical  Engineers,  1891. 

1513.  C.  E.  Guillaume.     His  articles  will  be  found  listed  in  some 

of  the  cross-references  cited. 

1514.  L.   Guillet.     "Steel  Used  for  Motor  Car  Construction  in 

France."  Journal  of  the  Iron  and  Steel  Institute,  No.  11, 
1905,  pages  166-203. 

1515.  L.  Guillet.     "The  Use  of  Vanadium  in  Metallurgy."     Same 

journal,  pages  118-165. 

For  Guillet's  other  memoirs  on  alloy  steels  consult  the 
Revue  de  Metallurgie,  and  the  index  of  the  Journal  of 
the  Iron  and  Steel  Institute  from  1904  to  date. 


ALLOY   STEELS  421 

1516.  J.  M.  Gledhill.     "The  Development  and  Use  of  High-speed 

Tool  Steel."  Journal  of  the  Iron  and  Steel  Institute,  No. 
11,  1904,  pages  127-182. 

1517.  H.  C.  H.  Carpenter.    "  High-speed  Tool  Steels."   Same  jour- 

nal, No.  1,  1905,  pages  433-473,  and  No.  Ill,  1906, 
pages  377-396. 

1518.  J.  T.  Nicolson.     "Experiments  with  Rapid-cutting  Steel 

Tools."  Manchester  Municipal  School  of  Technology, 
Manchester,  England,  1903. 

1519.  J.  Kent  Smith.     On  vanadium  steels;  see  Transactions  of 

the  American  Institute  of  Mining  Engineers,  vol.  xxxvii, 
1907,  pages  727-732.  Also  The  Iron  Trade  Review, 
November  7,  1907,  page  729.  Vol.  xli. 

1520.  (For  Vanadium  steels  see  also  the  index  of  the  Journal  of  the 

Iron  and  Steel  Institute,  especially  1905  to  date. 

1521.  L.  Guillet.     "  Quaternary  "Steels."    Journal  of  the  Iron  and 

Steel  Institute,  No.  11,  1906,  pages  1-141. 

1522.  For  all  the  alloy  steels  one  should  look  in  the  four  volumes 

of  Revue  de  Metallurgie,  for  which  see  No.  10,  at  end  of 
Chapter  I. 

1523.  De  Mozay.     "Etude  de  la  Durete  dans  les  Aciers  a  Outil  de 

Tour."  Revue  de  Metallurgie,  vol.  iv,  1907,  pages  885- 
900. 

1524.  Leon  Guillet.     "Nouvelles  Recherches  sur  les  Aciers  au 

Vanadium  Ternaires  et  Quarternaires."  Revue  de  Metal- 
lurgie, vol.  iv,  1907,  pages  775-783. 

1525.  P.  Nicolardot.     "Le  Vanadium."     Paris.     About  1906. 

1526.  A.J.Rossi.     "The  Metallurgy  of  Titanium."     Transactions 

of  the  American  Institute  of  Mining  Engineers,  vol.  xxxiii, 
1903,  pages  179-197,  with  cross-references. 

1527.  A.  J.  Rossi.     "  Titanif erous  Iron  Ores."     Engineering  and 

Mining  Journal,  vol.  Ixxviii,  1904,  pages  501  and  502. 

1528.  J.  Hoerhager.     "Ueber  titanhaltiges  Holzkohlen-Roheisen 

von  Turrach  in  Obersteiermark."  Oesterreichische  Zeit- 
schrift  fur  Berg-  und  Huettenwesen,  vol.  Hi,  1904,  pages 
571-577. 


XVI 
THE  CORROSION  OF  IRON  AND  STEEL 

IRON  offers  so  little  resistance  to  rusting  or  corrosion  that  there 
are  almost  no  circumstances  of  service  in  which  it  can  safely  be 
placed  without  some  means  of  protection  from  the  elements.  Cer- 
tain parts  of  machinery,  in  situations  where  rusting  is  not  very 
rapid  and  where  the  metal  will  receive  constant  cleaning  and  over- 
sight, are  used  without  any  protective  coating,  but  structural 
work,  in  and  outside  of  buildings,  tin  roofs,1  wire  fences,  pipes,  and 
other  metallic  structures,  all  require  to  be  protected  by  some 
coating,  such  as  paint,  galvanizing,2  tinning,  nickel  plating, 
oxidizing,  etc.  Boiler  tubes  and  the  inside  of  boilers,  tanks,  and 
pipes  it  is  usually  impossible  to  protect  by  paint,  galvanizing, 
etc.,  and  there  is  an  annual  loss  of  doubtless  many  thousands  of 
tons  of  iron  and  steel  from  the  decay  of  these  classes  of  articles 
alone. 

THE  CAUSE  AND  OPERATION  OF  CORROSION 

The  brown  powder  with  which  we  are  all  far  too  familiar  under 
the  name  of  rust  is  a  hydroxide  of  iron — ferric  hydroxide,  FeOsHs. 
It  is  formed  wherever  iron  is  exposed  to  the  action  of  water  and  air. 
Neither  dry  air  nor  water  free  from  oxygen  has  any  effect  upon  it 
alone,  but  as  air  is  always  moist  and  ordinary  water  contains  some 
oxygen  in  solution,  the  conditions  for  corrosion  practically  always 
prevail  against  the  iron  in  service.  The  alternate  attack  of  oxygen 
and  water  within  a  brief  period  is  far  more  destructive  than  the 
attack  of  either  one..  For  example,  heavy  rains,  the  splashing  of 
water  intermittently  upon  piers  and  columns,  the  rise  and  fall  of 
the  tide,  etc.,  corrode  the  metal  much  faster  than  exposure  all  the 

1  Tinplate  consists  of  a  thin  sheet  of  steel  or  wrought  iron  covered  with 
metallic  tin. 

2  I.e.,  coating  with  metallic  zinc. 

422 


THE  CORROSION   OF   IRON   AND   STEEL  423 

time  to  either  damp  air  or  oxygenated  water  alone.  Acids,  while 
not  essential  to  corrosion,  greatly  hasten  its  action,  so  that  the 
presence  of  carbonic  acid  in  the  air,  sulphurous,  sulphuric,  and 
hydrochloric  acids  in  the  smoke  from  locomotives  and  other  fires, 
all  greatly  increase  the  speed  of  rusting.  It  seems  evident  also 
that  at  least  some  weak  electrolysis  is  essential  for  any  corrosion  to 
occur.  I  shall  show  later  that  this  electrolytic  action  will  always 
take  place  where  iron  and  water  are  in  contact  with  each  other,  but 
it  is  very  small  in  amount  under  these  conditions.  Where  a  greater 
electric  force  exists,  as  for  example  where  pipe  lines  run  close  to 
trolley  tracks  and  receive  a  leak  of  electricity  so  as  to  carry  a  part 
of  the  current,  the  electrolytic  action  is  increased  and  corrosion 
much  hastened.  As  the  use  of  electricity  to-day  is  far  more  gen- 
eral than  ever  before  and  the  amount  of  coal  burned  and  conse- 
quently the  amount  of  corrosive  gases  in  our  atmosphere  is  much 
larger,  it  follows  that  the  question  of  corrosion  is  of  constantly  in- 
creasing importance.  Affairs  have  indeed  reached  such  a  state 
that  the  subject  is  now  occupying  a  great  deal  of  attention  from 
metallurgists  and  engineers  in  the  hope  of  getting  better  means  of 
protection.  Pipe  lines  embedded  in  the  earth,  which  are  alter- 
nately wet  and  dry,  supports  in  tunnels,  subways,  and  other  damp 
places,  wire  fences  and  tin  roofs  are  all  suffering  severely  from 
decay. 

Theories  of  Corrosion.  —  In  an  able  research,1  Allerton  S. 
Cushman  has  studied  the  current  theories  that  have  been  advanced 
to  account  for  the  corrosion  of  steel.  He  shows  that  the  theory 
that  carbonic  acid,  or  some  other  acid,  is  necessary  is  wrong,  and 
that  corrosion  will  take  place  even  in  weak  alkaline  solutions.  He 
also  shows  that  hydrogen  peroxide  is  not  the  agency  producing  the 
rust.  By  means  of  a  series  of  extremely  careful  and  accurate  ex- 
periments he  demonstrated  the  probability,  if  not,  indeed,  the  cer- 
tainty, that  the  two  factors  without  which  the  corrosion  of  iron  is 
impossible  are  electrolysis  and  the  presence  of  hydrogen  in  the 
electrolyzed  or  'ionic'  condition.  In  brief,  it  is  the  ions  of 
hydrogen  which  first  cause  the  metal  to  pass  in  solution: 

Fe  +  (4H  +  20)2=Fe02H2  +  H2 

Ions  of  hydrogen  are  electropositive  to  iron,  and  when  the  reaction 
takes  place,  they  transfer  their  electric  charge  to  the  metal.  This 

1  See  No.  160,  page  436.     2  4H+20  =2HaO  in  the  electrolyzed  condition. 


424  THE  METALLURGY  OF   IRON  AND  STEEL 

is,  of  course,  an  electrolytic  action  and  the  hydrogen  which  takes 
part  in  it  is  converted  from  the  electrolyzed  (or  ionic)  condition  to 
the  atomic  (or  gaseous)  condition.  Therefore  it  is  evident  that  the 
action  must  take  place  in  the  presence  of  oxygen,  or  some  other 
oxidizing  agent  that  will  complete  the  electrolysis,  else  the  forma- 
tion of  ferrous  hydroxide  will  soon  cease.  This  explains  why  the 
presence  of  oxygen  so  greatly  increases  the  corrosion  of  iron, 
although  it  is  not  the  oxygen  itself  which,  after  all,  is  the  cause  of 
the  primary  attack. 

Rust.  —  Ferrous  hydroxide,  FeC^H^,  is  soluble  in  water  and  its 
formation  and  solution  is  the  first  step  in  the  production  of  rust. 
Because  of  its  solubility,  however,  it  does  not  ordinarily  make  its 
presence  known  until  a  further  reaction  occurs : — 

2Fe02H2  +  H20  +  O  =2Fe03H3. 

The  rust,  FeOsHs,  so  formed  precipitates  from  solution. 

Unfortunately  traces  of  ionic  hydrogen  are  always  present  even 
in  the  purest  water,  and  larger  amounts  in  ordinary  water.  Sub- 
stances which  increased  the  hydrogen  ions,  such  as  oxides,  pro- 
mote the  rusting,  and  the  same  may  be  said  of  anything  which 
increases  the  electrolytic  action,  while  substances  which  restrain  the 
formation  of  hydrogen  ions  will  decrease  corrosion.  Indeed,  dip- 
ping a  piece  of  bright  iron  into  a  solution  of  potassium  bichromate 
and  then  wiping  it  off  will  put  it  into  an  apparently  oxidized  con- 
dition in  which  it  will  resist  corrosion  for  days  or  even  weeks. 
Cushman,  therefore,  suggests  dissolving  a  small  amount  of  chro- 
mic acid  or  potassium  bichromate  in  boiler  waters  in  order  to 
restrain  corrosion  of  the  metal. 

Segregation.  —  Evidently  anything  that  increases  the  electro- 
lytic activity  will  increase  the  attack  by  hydrogen  and  therefore 
the  formation  of  rust.  Unfortunately  even  the  purest  piece  of  iron 
will  show  differences  of  electric  potential  at  different  parts  and 
therefore  produce  an  electrolytic  effect.  When  the  metal  is  impure 
or  is  badly  segregated,  these  differences  in  potential  will  be  quite 
large,  and  when  several  pieces  of  steel  are  joined  together,  as  in  a 
bridge  or  other  structure,  the  difference  in  potential  between  the 
different  parts  may  be  great.  It  is  probable  that  each  of  the  dif- 
ferent microscopic  constituents  of  iron  and  steel  has  a  different 
electric  potential  and  therefore  either  assists  or  retards  the  progress 
of  rusting.  Also  scale,  the  slag  in  wrought  iron,  etc. 


THE  CORROSION   OF   IRON   AND   STEEL 


425 


Self-protection  from  Corrosion.  —  It  is  generally  believed  that 
certain  constituents  in  iron  and  steel  assist  in  protecting  underly- 
ing layers  of  the  metal  from  attack.  For  example,  the  graphite 
which  forms  such  a  large  proportion  (say  10%  or  more)  of  the 
volume  of  cast  iron,  slag  which  forms  nearly  4%  of  the  volume  of 
wrought  iron,  and  cementite 
in  steel,  all  corrode  less 
rapidly  than  the  pure  metal, 
and  it  is  probable  that  they 
are  beneficial  in  protecting 
it.  It  must  not  be  for- 
gotten, however,  that  they 
likewise  cause  a  difference 
in  potential  and  to  that  ex- 
tent probably  tend  to  hasten 
corrosion.  Their  net  effect 
can  be  learned  only  by  ex- 
periment. Scale  or  foreign 
substances  on  the  surface  of 
the  metal  would  also  pro- 
duce large  differences  in 
potential. 

Relative  Corrosion  of  Iron 
and  Steel.  —  It  is  generally 
believed  that  cast  iron  cor- 
rodes less  rapidly  than  either 
wrought  iron  or  steel  and, 
for  this  reason,  cast-iron  pipe 
is  greatly  preferred  for  city 
water  mains  and  like  uses 
where  great  strength  is  not 
required.  The  belief  is  a 

reasonable  one,  since  it  might  well  be  expected  that  the  pres- 
ence of  graphite  would  be  a  protection,  but  it  is  only  right  to 
remark  that  the  theory  rests  upon  no  experimental  evidence  and 
that  there  are  other  circumstances  connected  with  cast-iron  pipe 
which  may  not  have  given  rise  to  the  belief  but  which  are  not  in- 
herent in  the  material  itself.  These  conditions  are  (1)  the  common 
practice  of  dipping  cast-iron  pipe  in  asphaltum,  paint,  or  some  sim- 
ilar protecting  material,  before  it  is  sold  and  thus  putting  it  in  a 


FIG.    298.  —  CORRODED   STEEL    PLATE. 


426  THE  METALLURGY   OF   IRON  AND   STEEL 

condition  to  be  in  service  for  a  long  time  before  the  metal  itself  is 
subjected  to  the  corrosive  influences.  (2)  When  the  iron  is  cast 
in  the  sand  there  seems  to  take  place  some  union  between  the 
metal  and  the  inside  surface  of  the  mold,  whereby  a  very  resisting 
siliceous  coating  or  'skin'  is  formed  on  the  casting.  Some  be- 
lieve that  after  this  skin  is  worn  away,  cast  iron  corrodes  as  rapidly 
as  wrought  iron  or  steel.  (3)  Cast-iron  pipe  is  thicker  than  the 
same  diameter  of  wrought  iron  and  steel  pipe,  because  of  the 
difficulty  of  making  castings  with  thin  sections  of  metal ;  therefore 
such  pipe  would  remain  in  service  much  longer  than  steel  or 
wrought  iron,  even  though  the  rate  of  corrosion  were  the  same. 
I  have  cited  the  above  facts  not  to  argue  against  the  belief  in  the 
slow  corrosion  of  cast  iron,  but  merely  to  explain  the  situation  as 
it  exists,  for  we  have  as  yet  no  scientific  data  upon  which  to  form 
an  opinion  either  way. 

Wrought  Iron  vs.  Steel.  —  There  is  also  a  very  prevalent  and 
widespread  conviction  that  steel  corrodes  much  more  rapidly  than 
wrought  iron.  This  opinion  too  rests  upon  no  very  exact  experi- 
mental evidence,  although  there  are  not  incidents  lacking  which 
make  in  favor  of  it,  while  others  make  in  the  opposite  direction,  but 
it  seems  to  be  based  principally  upon  the  fact  that  corrosion  is  very 
much  more  rapid  to-day,  when  steel  is  the  world's  great  metal, 
than  it  was  some  years  ago  when  wrought  iron  was  chiefly  used! 
But  I  have  already  shown  that  conditions  to-day  are  more  con- 
ducive to  rapid  corrosion  than  they  were  at  any  previous  time.1 

Opposed  to  this  popular  belief  is  the  result  of  a  great  many 
scientific  tests  which  have  shown,  in  almost  every  case,  that  the 
difference  in  the  speed  of  corrosion  between  wrought  iron  and  steel 
is  very  small,  although  favorable  to  wrought  iron  in  the  case  of 
sea  water  and  alkaline  water  and  to  steel  in  the  case  of  acids  and 

1  Indeed  I  hardly  think  that  this  argument  ought  to  have  anything  like  the 
weight  that  is  popularly  given  to  it.  It  is  not  at  all  uncommon  to  hear  the  state- 
ment that  wrought  iron  made  20  years  ago  is  still  in  service  in  places  and  con- 
ditions alongside  of  steel  which  has  been  replaced  several  times.  But  I  am 
informed  by  a  testing  engineer  of  much  experience  and  reputation  that  he  has 
a  steel  fence  upon  his  property  which  has  been  in  service  many  years  and  has 
outlasted  several  other  steel  fences  under  similar  conditions,  but  formed  of  steel 
made  recently.  From  this  he  argues  that  the  steel  made  to-day  is  more  sub- 
ject to  corrosion  than  the  steel  made  many  years  ago.  If  this  is  so,  we  are 
permitted  to  ask:  Is  the  wrought  iron  made  to-day  more  subject  to  corrosion 
than  the  wrought  iron  made  several  years  ago? 


THE  CORROSION   OF   IRON  AND   STEEL 


427 


acidulated  water.  As  has  been  pointed  out,  however,  these 
scientific  tests  are  not  altogether  reliable  as  a  basis  for  commer- 
cial comparison,  because  they  have  not  usually  been  carried  to 
the  point  where  either  one  material  or  the  other  becomes  unfit  for 
service,  but  merely  allow  corrosion  to  proceed  for  several  months 
and  then  show  the  rela- 
tive loss  in  weight. 
Neither  have  these  ex- 
periments taken  into 
account  sufficiently  the 
localized,  i.e.,  "pitting," 
corrosion  to  which  badly 
made  material  is  especi- 
ally subject.  It  is  im- 
material whether  or  not 
the  metal  has  lost  but 
little  weight,  provided 
it  has  pitted  in  any 
one  spot  sufficiently  to 
fail,  or  to  have  become 
dangerously  thin.  This 
pitting  is  believed  to  be 
due  chiefly  to  blowholes 
and  possibly  to  segrega- 
tion resulting  in  a  local 
increase  in  electric  po- 
tential. 

Manganese  and  Cor- 
rosion. —  It  has  been 
suggested  that  the  pres- 
ence of  manganese  in 
steel  causes  an  increase 
in  the  rate  of  corrosion,  but  this  assertion  is  based  upon  no  reliable 
evidence  so  far  as  I  am  aware.  It  was  brought  forward  to  ex- 
plain the  supposed  rapid  corrosion  of  steel  as  compared  with 
wrought  iron,  but  if  it  is  a  true  influence  in  this  direction,  then  steel 
should  corrode  in  acids  faster  than  wrought  iron,  which  it  appar- 
ently does  not  if  the  steel  has  been  made  with  due  care  and  is  free 
from  blowholes  and  much  segregation. 

Badly  Made  Material.  —  There  can  be  no  doubt  that  badly 


FIG.  299.  —  CORRODED  WROUGHT-IRON 
PLATE. 


428  THE  METALLURGY  OF   IRON  AND   STEEL 

made  steel  is  much  more  liable  to  corrosion  and  to  pitting  than  well- 
made  steel,  and  it  may  be  from  this  cause  that  the  bad  name  which 
steel  is  popularly  given  comes.  There  can  also  be  no  doubt  that 
badly  made  wrought  iron  is  extraordinarily  subject  to  rusting, 
and  of  this  kind  of  material  we  are  to-day  getting  a  good  deal.  As 
I  have  noted  in  Chapter  III,  probably  more  than  half  of  the  wrought 
iron  produced  in  America  is  made  by  '  busheling '  scrap  into  a  pile, 
rolling  it  down  and  marketing  it  as  wrought  iron.  This  material 
is  of  good  quality  so  long  as  the  scrap  from  which  it  is  made  is 
good,  but  when  the  scrap  is  collected  from  almost  any  source, 
and  especially  when  it  contains  steel,  as  it  sometimes  does,  we 
should  expect  great  differences  in  potential  and  therefore  rapid 
corrosion. 

Coating.  —  Wrought  iron  has  one  advantage  over  steel  in  the 
case  of  articles  which  are  to  be  coated,  because  its  rough  surface 
gives  a  better  opportunity  for  the  paint  to  adhere  than  the  com- 
paratively smooth  and  even  surface  of  steel. 

Summary.  —  Badly  made  steel  and  badly  made  wrought  iron 
corrode  faster  than  any  other  material;  next  in  order  come  well- 
made  steel  and  well-made  wrought  iron,  between  which  two  classes 
the  difference  is  probably  very  slight,  and  has  not  been  determined 
by  any  sufficiently  lengthy  or  convincing  series  of  tests;  the  next  in 
order  is  probably  cast  iron,  although  as  yet  we  cannot  be  quite 
certain  that  this  corrodes  more  slowly  than  wrought  iron  and 
steel,  except  in  so  far  as  it  is  protected  by  its  natural  or  artificial 
coating  or  both.  Steel  and  wrought  iron  are  both  liable  to  pitting, 
which  may  greatly  shorten  their  life  in  service  even  though  the 
average  rate  at  which  they  corrode  is  slow.  Several  causes  may 
produce  this  pitting,  such  as,  blowholes,  segregation,  bad  welding 
in  places,  particles  of  oxide,  scale  or  dirt,  etc.  When  pits  or  holes 
are  found  with  a  smooth,  hollow  surface,  it  is  altogether  probable 
that  they  are  due  to  blowholes  and  sometimes  these  pits  may  be  an 
inch  or  more  in  diameter  and  extend  an  eighth  of  an  inch  into  the 
plate,  even  before  the  remainder  of  the  surface  has  become  severely 
attacked.  Numerous  efforts  are  being  made  at  the  present  time  to 
improve  the  quality  of  steel  and  to  turn  out  a  more  uniform  grade 
of  product.  It  is  quite  certain  that  painting  is  not  as  good  to-day 
as  it  was  in  years  past  and  that  the  quality  of  paint  used  is  also 
worse,  on  the  average,  as  shown  by  the  fact  that  paint  does  not 
last  as  well  on  wooden  structures.  The  better  adherence  of  paint 


THE  CORROSION  OF   IRON  AND  STEEL  429 

gives  an  advantage  to  wrought  iron,  which -however,  only  applies 
where  work  is  so  placed  as  to  be  capable  of  being  painted. 

PRESERVATIVE  COATINGS  FOR  IRON  AND  STEEL 

The  oxidized  surface  which  all  steel  retains  after  hot  working 
is  in  itself  a  certain  protection  against  corrosion,  but  this  is  only 
limited  in  effect,  because  the  oxide  is  more  or  less  porous  and  so 
allows  the  corrosive  agencies  to  penetrate  it  and  attack  the  surface 
underneath.  Moreover,  the  scale  does  not  adhere  firmly  in  some 
places,  and  as  its  coefficient  of  expansion  and  contraction  is  dif- 
ferent from  that  of  the  metal,  it  is  liable  to  loosen  and  fall  off  in 
places  and  so  expose  the  iron  or  steel. 

Preparation  of  Surfaces  for  Coating.  —  It  is  not  advisable  to 
coat  wrought  iron  or  steel  until  its  surface  has  been  carefully  pre- 
pared, for  any  rust  or  other  product  of  corrosion,  scale,  grease, 
dirt,  or  moisture  underneath  the  coat  will  either  start  corrosion  or 
else,  by  becoming  loosened,  will  cause  the  paint  or  galvanizing  to 
fall  off  and  so  expose  the  metal  underneath.  The  opposite  is  the 
case  with  cast  iron,  because  when  this  metal  is  poured  liquid  into 
the  mold  a  skin  is  formed,  consisting  of  a  chemical  union  of  silica 
and  oxide  of  iron,  very  firmly  united  to  the  metal  and  capable  of 
being  relied  upon  to  adhere  beneath  the  paint  or  other  coating  and 
serve  as  additional  protection  from  corrosion.  So  much  mill  scale 
as  adheres  to  wrought  iron  and  steel  with  great  force  is  permitted 
by  some  engineers  to  remain  underneath  the  protective  coating, 
but  others  insist  upon  the  removal  even  of  this  upon  the  ground 
that  it  may  become  loosened  later  by  expansion  and  contraction, 
and  then  spall  off. 

Priming  Coat.  —  A  difference  of  opinion  exists  as  to  the  ad- 
visability of  having  wrought-iron  and  steel  surfaces  prepared  at 
the  mill  and  there  given  a  priming  coat,  or  else  having  the  priming 
coat  applied  under  the  direction  of  the  engineer  of  construction,  or 
else  of  omitting  the  priming  coat  altogether  and  not  painting  the 
structure  at  all  (except  such  parts  of  it  as  will  be  inaccessible  after 
erection)  until  the  metal  has  been  exposed  so  long  that  the  weather 
has  loosened  all  the  scale.  This  will  occupy  perhaps  six  months  to 
a  year,  depending  upon  the  corrosive  conditions.  During  that  time 
no  great  damage  can  be  done  by  corrosion  although  the  structure 
will,  of  course,  look  very  shabby.  After  that  period,  the  scale  is 


430  THE  METALLURGY   OF   IRON  AND   STEEL 

removed  with  sand  blast,  wire  brushes,  pneumatic  hammers,  or 
chisels,  and  after  the  surface  is  perfectly  clean  and  dry,  it  is  given  a 
priming  coat  and  at  least  two  other  good  coats  of  paint,  each  one 
being  allowed  to  dry  thoroughly  before  the  next  is  spread.  For 
indoor  work  one  coat  of  paint!  upon  the  priming  coat  is  often  con- 
sidered sufficient. 

Shop  vs.  Field  Painting.  —  The  advantage  of  painting  the  steel 
at  the  shop  is  that  it  can  be  done  inside  of  some  building  and  there 
is  therefore  less  liability  of  hygroscopic  moisture  under  the  coating. 
If  the  shop  coat  is  put  on  with  care  and  skill  it  unquestionably  has 
certain  advantages,  but  it  is  too  true  that  the  shop  painting  and  the 
preparation  of  surfaces  at  the  shop  is  often  carelessly  done,  for  the 
manufacturer  has  not  the  interest  in  preserving  the  metal  from 
decay  that  the  consumer  feels.  Furthermore  it  undoubtedly 
saves  expense  to  allow  the  structure  to  stand  from  six  months  to  a 
year,  provided  that  it  is  then  very  thoroughly  cleaned  and  well 
painted  when  absolutely  dry.  If  otherwise  the  whole  work  may 
have  to  be  done  over  again  at  the  end  of  a  short  interval.1 

Pickling.  —  To  remove  scale  it  is  customary  in  many  cases  to 
pickle  the  steel  or  wrought  iron,  i.e.,  to  immerse  it  in  dilute  sul- 
phuric acid  (say  10  per  cent.)  preferably  heated  to  boiling  so  as  to 
act  more  quickly.  After  a  few  minutes  the  scale  is  removed,  when 
the  metal  is  washed  once  in  boiling  water,  once  in  cold  water,  and 
finally  in  lime  water  to  neutralize  the  last  traces  of  the  acid.  It 
should  remain  in  the  lime  water  until  it  is  ready  for  the  application 
of  the  coating,  when  it  should  first  be  washed  free  of  lime,  and  then 
heated  slightly  above  100°  C.  (212°  F.)  to  drive  off  all  the  moisture. 
Pickling  is  therefore  applicable  only  when  the  metal  is  to  be  coated 
at  the  shop,  either  with  the  priming  coat  of  paint  or  with  zinc,  tin, 
etc. 

Comparison  of  Methods.  —  Pickling  costs  less  than  the  other 
methods  of  removing  scale  and  accomplishes  the  work  very  thor- 
oughly. Sand  blast  is  the  next  cheapest  method.  This  latter 
does  not  get  off  all  the  scale  unless  it  is  very  thorough,  while,  if  it  is 
too  thorough,  it  leaves  the  surface  in  a  smooth  condition  so  that  the 
paint  does  not  stick  so  well.  On  the  other  hand,  pickling  must  be 
done  with  great  care  or  it  may  leave  hydrogen  upon  the  surface  of 
the  metal  which  will  greatly  hasten  corrosion,  so  that  pickled 

1  In  which  event  it  is  customary  for  all  interested  parties  to  blame  the 
paint,  except  the  paint-maker  who  is  in  the  minority. 


THE  CORROSION   OF   IRON   AND   STEEL  431 

surfaces  sometimes  corrode  more  rapidly  than  those  which  have 
been  cleaned  in  any  other  way.  Cleaning  with  wire  brushes  is  more 
expensive  than  sand  blasting,  but  if  performed  with  great  care  is 
more  effective  and  leaves  the  surface  in  a  rougher  condition  which 
assists  the  adherence  of  the  paint. 

Kinds  of  Paint  Used.  —  There  is  a  great  difference  of  opinion  as 
to  the  best  paint  for  preserving  iron  and  steel,  but  some  few  things 
seem  certain:  (1)  That  no  one  kind  of  paint  is  suitable  protection 
against  all  corrosive  influences.  For  example,  the  best  paint  to 
withstand  the  action  of  the  open  air  may  fail  when  exposed  to  the 
elements  in  a  damp  tunnel,  or  when  used  on  the  parts  of  piers 
under  sea  water,  while  a  good  protection  against  this  latter  influ- 
ence might  be  inefficient  when  exposed  to  the  oxidizing  gases  in 
locomotive  smoke,  etc. ;  (2)  that  whatever  paint  is  used  must  be 
sufficiently  elastic  to  expand  and  contract  with  the  changes  in 
temperature  of  the  metal  without  'cracking;  and  (3)  that  it  must 
contain  nothing  which  will  attack  the  metal  and  so  commence  cor- 
rosion. In  this  last  connection  we  must  especially  avoid  all  oxidiz- 
ing influences.  The  reader  will  find  in  the  Annual  Proceedings  of 
the  American  Society  for  Testing  Materials  a  very  full  interchange 
of  opinions  between  experts  in  paint  manufacture  and  engineering 
which  will  doubtless  help  him  to  form  an  opinion  as  to  the  best 
paint  to  use  in  each  case. 

There  are  two  parts  to  every  paint:  (1)  The  vehicle  which  car- 
ries the  pigment  and  undergoes  a  change  to  the  solid  state  when  the 
paint  dries,  and  (2)  the  pigment  or  originally  solid  part  of  the  pre- 
servative coating.  These  two  must  form  a  firm  impervious  coat- 
ing upon  the  surface  of  the  metal,  but  must  not  be  so  solid  as  to  be 
inelastic  or  brittle. 

Linseed  Oil.  —  Linseed  oil  is  a  very  good  and  common  vehicle.1 
It  is  what  is  known  as  a  '  drying  oil.'  That  is  to  say,  an  oil  which 
when  exposed  to  the  atmosphere  will  change  from  a  liquid  to  an 
elastic  or  leathery  consistency.  This  action  takes  place  not  by 
evaporation  but  by  a  process  of  oxidation,  whereby  the  oil  absorbs 
oxygen  to  the  extent  of  from  10  to  18  per  cent,  of  its  weight  and  ex- 
pands in  volume,  so  that  a  coat  of  linseed  oil  spread  upon  glass  will 
wrinkle  up  upon  drying.  It  is  because  linseed  is  the  best  of  all  the 
drying  oils  that  it  is  so  much  preferred  as  a  paint  vehicle,  but  when 
allowed  to  dry  in  the  raw  state  it  requires  too  long  a  time  and  the 
1  See  page  336  of  No.  163 ;  page  41  of  No.  164,  page  436'. 


432  THE  METALLURGY  OF   IRON  AND   STEEL 

drying  is  therefore  hastened  by  boiling  it  and  adding  some  oxidizing 
agent,  known  as  a '  drier/  of  which  the  best,  as  far  as  iron  and  steel 
preservation  is  concerned,  are  the  salts  of  lead  or  manganese,  used 
without  rosin.  It  will  readily  be  understood  how  dangerous  it  is  to 
indiscriminately  use  driers  (i.e.,  oxidizing  agents)  in  steel  paints, 
because  so  many  of  them  will  oxidize  the  steel  and  so  cause  the  very 
corrosion  which  it  is  the  object  of  the  paint  to  prevent. 

Purity  of  Linseed.' —  This  brings  us  to  the  question  of  the  purity 
of  linseed  oil,  for  the  usual  adulterants  are  all  harmful  to  steel  work 
and  cause  in  the  end  more  painting  and  more  of  the  expensive 
cleaning  of  structures  to  receive  the  coating,  out  of  all  proportion 
to  their  lesser  first  cost.  Freedom  from  adulterants  probably 
cannot  be  obtained  except  by  constant  watchfulness  and  frequent 
chemical  analysis  on  the  part  of  the  consumer.  Some  impurity 
arises  from  the  presence  of  a  few  per  cent,  of  foreign  seeds  with  the 
linseed,  which  is  not  always  avoidable,  but  the  greater  harm  comes 
from  the  fact  that  the  oil  is  obtained  from  the  linseed  by  pressing  it 
while  hot,  in  which  way  a  larger  amount  of  product  is  extracted 
than  if  cold  pressure  is  applied,  because  some  of  the  solid  part  of  the 
seeds  are  thereby  extracted  together  with  the  oil.  Cold  pressed 
linseed  oil  has  a  golden  yellow  color  and  remains  clear  in  cold 
weather  as  distinguished  from  the  yellowish-brown  color  of  the  hot 
pressed  oil  which  also  has  a  more  acrid  taste,  is  not  so  fluid,  and  con- 
tains more  solid  fats,  solid  organic  matter,  and  fatty  acids,  all  of 
which  are  harmful  either  because  they  attack  the  metal  or  else 
because  they  make  a  pervious  paint. 

Pigments.  —  The  pigment  is  not  as  important  as  the  vehicle 
and  many  different  ones  can  be  chosen,  provided  they  are  chemic- 
ally inert  to  the  steel.  Red  lead  has  been  very  much  used  and  is 
very  good  especially  for  the  priming  coat,  for  it  seems  to  form  with 
the  linseed  oil  a  very  dense,  impervious  coating.  For  the  outer 
coats,  however,  it  is  generally  well  to  mix  the  red  lead  with  some 
substance  that  shall  reduce  its  weight,  such  as  graphite.  Ferric 
oxide,  Fe2O3,  and  other  oxides  of  iron  in  the  form  of  iron  ore  are 
very  cheap  and  withstand  the  action  of  sulphur  gas  better  than  the 
red-lead  paints.  They  are  very  good  for  outer  coats  where  loco- 
motive smoke  and  similar  gases  are  liable  to  be  present.  Sulphate 
of  lead,  white  lead  (a  mixture  of  oxide  and  sulphate  of  lead  with 
often  some  sulphate  of  zinc)  and  sulphate  of  zinc  are  all  good  white 
paints  although  expensive.  Pulverized  asphaltum  and  other 


THE  CORROSION   OF   IRON  AND   STEEL  433 

hydrocarbons  are  also  used  with  success  as  pigments,  especially 
where  the  metal  is  exposed  in  damp  ground  or  under  water. 

Other  Paints.  —  Pipe  is  often  coated  very  cheaply  by  dipping 
it  in  melted  asphaltum  or  pitch.  The  objection  to  this  coat  is  that 
it  is  very  hard  and  brittle  when  cold  and  in  time  it  forms  a  network 
of  myriads  of  cracks  through  which  the  atmosphere  attacks  the 
metal.  For  cast-iron  pipe  it  is  very  useful,  however,  because  this 
is  protected  by  its  natural  skin.  Dipping  in  tar  would  form  an 
elastic  coating,  but  unfortunately  tar  contains  certain  acids  and 
oxidizing  agents  which  attack  the  metal.  There  is  a  paint  made 
by  distilling  off  the  creosote  and  other  volatile  components  of  tar 
until  the  solid  asphaltum  is  left.  This  is  then  redissolved  in 
two  of  the  distillates,  neither  of  which  will  attack  iron  work, 
and  thus  a  paint  is  obtained  which  is  said  to  be  practically  tar 
without  any  of  its  harmful  constituents.  It  forms  a  very  elastic 
coating  which  does  not  crack  after  years  of  exposure  nor  does  it 
disintegrate  under  the  action  of  the  sun  as  the  linseed  oil  paints 
sometimes  do. 

Galvanizing.  —  Galvanizing  is  the  process  of  coating  with 
metallic  zinc  and  where  this  coating  adheres  firmly,  it  undoubtedly 
forms  a  very  efficient  means  of  protecting  iron  from  corrosion.  As 
zinc  is  electrically  positive  towards  iron,  whatever  electrolysis 
exists  would  tend  to  corrode  the  zinc  and  protect  the  iron.  In- 
deed this  fact  is  taken  advantage  of  by  some  engineers  who  hang 
pieces  of  zinc  in  their  boilers,  by  means  of  a  wire  connected  to  the 
steel  work,  so  that  the  electrolytic  action  shall  corrode  the  zinc  and 
protect  the  wrought  iron  or  steel. 

Galvanizing  is  usually  applied  to  wire  and  wire  products,  thin 
sheets,  especially  corrugated  sheets  used  for  the  outside  of  build- 
ings, etc.,  tubes,  hollow  ware,  and  a  great  variety  of  articles,  after 
the  surfaces  have  been  cleaned  by  pickling.  There  are  three 
methods  by  which  the  galvanizing  is  effected,  known  respectively 
as  cold  galvanizing,  hot  galvanizing,  and  dry  galvanizing. 

Cold  Galvanizing.  —  In  the  cold  galvanizing  process  zinc  is  de- 
posited electrolytically  upon  the  surface  of  metallic  articles  which 
are  made  the  cathode  of  an  electro-plating  cell.  The  zinc  is  first 
dissolved  in  sulphuric  acid  and  water  and  this  solution  is  made  the 
electrolyte.  The  anode  is  a  piece  of  zinc,  so  that  as  fast  as  the  elec- 
tricity deposits  zinc  upon  the  surface  of  the  article  being  galvan- 
ized, it  replenishes  the  electrolyte  by  dissolving  zinc  from  the  anode. 


434  THE  METALLURGY  OF   IRON  AND   STEEL 

The  coating  is  about  0.0003  to  0.0005  inch  thick,  equivalent  to 
about  0.2  to  0.3  ounce  of  zinc  per  square  foot  of  surface. 

Hot  Galvanizing.  —  In  the  hot  galvanizing  process,  which  is  the 
commonest  one  used,  the  articles  to  be  galvanized  are  dipped  into 
a  bath  of  molten  zinc  at  a  temperature  of  425°  to  460°  C.  (800°  to 
860°  F.),  i.e.,  slightly  above  the  melting  point  (419°  C.  =786°  F.). 
The  metal  is  exposed  to  the  zinc  bath  usually  about  1J  to  7J 
minutes,  depending  upon  the  thickness  of  coating  desired,  which 
will  vary  between  0.0003  and  0.0010  inch  or  about  0.2  to  0.6  ounce 
of  zinc  per  square  foot  of  surface  covered,  or  about  0.3  to  0.6  ounce 
per  pound  of  wire.  In  the  case  of  wire  the  iron  or  steel  is  drawn 
slowly  through  the  bath  of  melted  zinc  and  usually  passes  over  a 
wiper  as  it  comes  out,  which  removes  the  still  molten  zinc  and 
causes  the  zinc  remaining  to  stick  a  little  more  firmly  and  have  a 
more  uniform  thickness.  The  coating  on  this  wiped  wire  is  not 
so  liable  to  crack  and  break  off  when  the  wire  is  bent  and  twisted 
as  the  coat  of  unwiped  wire  but,  on  the  other  hand,  it  is  thinner 
and  gives  but  little  protection  against  corrosion.  Sometimes  arti- 
cles to  be  galvanized  are  first  dipped  in  a  bath  of  melted  lead  and 
then  in  the  melted  zinc.  This  gives  a  cheaper  coating. 

Dry  Galvanizing.  —  The  process  of  dry  galvanizing  is  a  recent 
invention  and  consists  in  heating  the  articles  to  be  galvanized  in- 
side a  closed  vessel  and  while  they  are  covered  with  what  is  known 
as  'blue  powder/  which  is  a  zinc  dust  containing  some  oxide  of 
zinc  and  relatively  cheap  in  price  because  it  is  a  by-product  in  the 
metallurgy  of  zinc.  The  temperature  is  about  300°  C.  (575°  F.), 
and",  although  this  is  below  the  melting  point  of  zinc  and  of  iron,  it  is 
sufficiently  high  to  produce  an  alloy  between  the  two,  forming,  it 
is  said,  a  very  resisting  coating  which  is  more  thoroughly  attached 
to  the  surface  of  the  metal  and  therefore  much  more  durable 
against  cracking  off. 

Comparison  of  Galvanizing  Methods. — Cold  galvanizing  depos- 
its a  thinner  coating  of  zinc  which,  if  improperly  performed,  is 
liable  to  be  porous  or  spongy,  but  it  gives  a  better  connection  be- 
tween iron  and  zinc  and  therefore  a  more  durable  coating.  Hot 
galvanizing  necessitates  the  use  of  a  flux  on  the  bath  of  melted 
zinc  in  order  that  the  zinc  may  not  be  oxidized  by  air,  and  these 
fluxes  probably  have  the  effect  of  sometimes  beginning  the  corrosion 
of  the  iron  underneath  the  layer  of  zinc.  The  process  of  dry  gal- 
vanizing is  too  new  yet  for  any  comparison  to  be  drawn. 


THE  CORROSION  OF   IRON  AND  STEEL  435 

Tinning.  —  A  large  amount  of  metal  is  coated  with  tin  in  order 
to  give  protection  against  organic  acids,  such  as  those  present  in 
cooked  foods,  and  also  in  order  to  give  a  more  effective  resistance 
to  the  elements.  Thus  cooking  utensils,  roofing  sheets,  tin  cans 
for  preserves,  and  many  such  articles  are  coated  with  tin  in  pref- 
erence to  zinc,  either  because  zinc  would  not  withstand  so  long 
the  corrosive  influence,  or  else  would  not  resist  it  at  all.  In  the  tin- 
ning operations  the  metal  sheets  are  usually  drawn  through  a  bath 
of  liquid  tin  by  four  to  six  pairs  of  rolls  which  are  immersed  in  it. 
Each  pair  of  rolls  presses  the  tin  which  has  solidified  on  the  surface 
of  the  iron  firmly  upon  the  metal  and  the  result  is  a  smooth,  bright, 
adhering  coat  which  protects  the  metal  very  successfully.  Tin 
plating  is  more  expensive  than  galvanizing,  chiefly  on  account  of 
the  additional  cost  of  the  tin. 

Terne  Plate.  —  Sometimes  sheet"  metal  is  coated  with  a  mixture 
of  two-thirds  lead  and  one-third  tin  and  then  goes  under  the  name 
of  terne  plate,  which  is  used  very  largely  for  roofing  and  outdoor 
purposes.  It  is  applied  by  the  same  method  as  tinning  but  is 
less  expensive. 

Nickel  Plating.  —  Articles  requiring  a  very  high  polish  and 
which  are  to  be  subjected  to  handling,  etc.,  are  often  plated  with 
nickel.  This  is  an  electrolytic  process,  similar  to  the  general  oper- 
ation described  under  the  electrolytic  galvanizing.  Nickel  plating 
is  more  expensive  than  galvanizing  or  tinning,  but  gives  a  more 
highly  resisting  surface. 

Oxidized  Coating.  —  There  are  one  or  two  processes  by  which  a 
black  oxidized  surface  can  be  given  to  iron  and  steel  which  will  re- 
sist rust  for  years  and  form  what  are  known  as  '  black  iron '  objects. 
It  is  used  chiefly  for  fancy  iron  work  in  house  decorations,  etc. 

Enameling.  —  A  number  of  articles,  such  as  bath  tubs,  wash- 
bowls, cooking  utensils,  are  made  of  cast  iron  or  steel  and  then 
coated  with  a  white  or  variously  colored  film  known  as  enamel. 
Enameling  processes  are  more  or  less  secret,  but  usually  consist  in 
powdering  the  enamel  upon  the  surface  of  the  metallic  article  which 
has  been  heated  to  a  red  heat.  At  this  temperature  the  mixtures 
forming  the  enamel  melt  and  spread  themselves  uniformly  over 
the  surface  where  they  chill  and  harden.  Enamel  must  be  in- 
soluble in  water  and  in  chemicals  with  which  they  are  liable  to  come 
in  contact,  and  must  also  be  sufficiently  elastic  to  expand  and  con- 
tract with  the  metal  without  breaking  off. 


436  THE  METALLURGY  OF   IRON  AND  STEEL 


REFERENCES  ON  CORROSION 

See  especially  Nos.  117,  118,  and 

160.  Allerton  S.  Cushman.     "The  Corrosion  of  Iron."     Proceed- 

ings of  the  American  Society  for  Testing  Materials,  vol.  vii, 
1907,  pages  211-228.  Same  published  as  Bulletin  No.  30, 
Department  of  Agriculture,  Washington,  D.  C.  With  many 
cross-references. 

161.  Henry  M.  Howe.     "Relative  Corrosion  of  Wrought  Iron  and 

Steel."  See  Proceedings,  International  Association  for 
Testing  Materials,  1900,  vol.  xi,  Part  I,  pages  229-266. 
Paris,  1901.  Abstracted  in  No.  162,  and  in  Journal  Iron 
and  Steel  Institute,  No.  11,  1900,  pages  567,  568. 

162.  Frank  N.  Speller.     "Steel  and  Iron  Wrought  Pipe."     The 

Iron  Age,  March  2,  1905,  vol.  Ixxv,  pages  741-745.     With 
several  cross-references  on  relative  corrosion. 
See  also  the  indices  of  No.  8  for  abundant  references. 

163.  J.   Lewkowitsch.     "Chemical   Analysis   of   Oils,   Fats   and 

Waxes."     London,  1898. 

164.  A.  H.  Church.     "The  Chemistry  of  Paints  and  Painting." 

London,  1901. 


XVII 
THE    ELECTRO-METALLURGY    OF    IRON    AND    STEEL 

IN  the  electric  smelting  and  refining  of  iron  and  steel,  four 
modifications  in  practice  are  produced: 

1.  Practically   any   desired   temperature  in   reason   may   be 
obtained. 

2.  The  impurities  introduced  with  the  usual  fuels  are  avoided. 

3.  The  temperature  is  regulated  with  much  greater  accuracy. 

4.  The  cost  of  the  processes  is  increased. 

For  many  years  the  first  three  modifications  have  been  taken  ad- 
vantage of  in  the  production  of  ferro-alloys  —  e.g.,  ferro-tungsten 
ferro-chrome,  ferro-molybdenum,  etc.  —  that  is,  alloys  of  pig  iron 
and  some  other  metal  which  is  used  for  recarburizing  in  the 
manufacture  of  alloy  steels.  The  high  temperature  necessary 
for  the  production  of  these  alloys  gives  electric  smelting  especial 
advantages  while  the  high  price  at  which  they  can  be  sold  enables 
their  manufacturers  to  stand  the  additional  expense  with  profit. 
But  in  the  year  1900  a  number  of  important  electro-metallurgists  in 
Europe  and  America  began  to  use  electric  processes  for  the  pro- 
duction of  pig  iron  and  steel  on  a  commercial  scale,  and  from  this 
time  the  industry  dates.  Because  the  electric  processes  have 
apparently  secured  for  themselves  a  permanent  place  in  the 
metallurgy  of  iron  and  steel,  and  because  of  the  great  interest 
which  they  have  evoked,  I  have  decided  to  devote  some  space  to 
them  here,  although  the  amount  of  metal  produced  by  them  is 
still  very,  very  small  in  comparison  with  the  older  methods. 

Iron  and  steel  electro-metallurgical  processes  naturally  divide 
themselves  into  three  classes: 

(1)  Ore  smelting  for  the  production  of  pig  iron. 

(2)  Refining  of  pig  iron  to  produce  steel,  and 

(3)  Electrolytic  refining  of  steel  or  wrought  iron  to  produce 
almost  chemically  pure  iron. 

The  first  two  classes  are  electro-thermic;  that  is  to  say,  they 
use  electricity  for  conversion  into  the  heat  necessary  for  smelting; 

437 


438 


THE  METALLURGY  OF   IRON  AND   STEEL 


the  third  class  is  electrolytic,  that  is  to  say,  the  electric  current 
serves  to  produce  chemical  changes. 

ELECTRO-THERMIC  ORE  SMELTING 

The  two  most  successful  ore-smelting   processes  are  those  of 
Heroult  and  Keller,  and  in  each  of  those  the  furnace  is  filled  with 

the  charge,  consisting  of  ore, 
flux,  and  coke  which  resembles 
the  ordinary  blast  -  furnace 
charge,  except  that  the  amount 
of  coke  is  much  smaller  since 
the  electricity  is  relied  upon 
for  the  production  of  heat. 
No  blast  is  driven  into  those 
furnaces,  but  a  powerful  cur- 
rent of  electricity  is  passed 
through  the  charge,  the  high 
resistance  of  which,  on  account 
of  its  poor  conductivity,  pro- 
duces a  great  deal  of  heat. 
The  degree  of  heat  can  be  reg- 
ulated both  by  the  intensity 
of  the  current  and  the  charac- 
ter of  the  charge,  in  which  the 
coke  is  the  best  conductor. 
The  process  will  be  better  un- 
derstood by  reference  to  Figs. 
300  and  301,  and  the  descrip- 
tions thereunder.  When  a 
certain  temperature  is  reached 
the  carbon  reduces  the  ore, 
and  the  iron  thus  produced 
absorbs  from  the  coke  carbon, 
silicon,  sulphur  and  phos- 
phorus,1 and  collects  in  a 

conducted  mainly  by  the  coke,  which  is  heated     ^       -j  j      t    ^      bottom    of 

on  amount,  nf   its   fiWtrioa.1    resistance,  and    to  T. 

the     furnace.       The     gangue 
unites  with  the  flux  to  form  a 
1  Some  phosphorus  is  absorbed 
from  the  ore  also. 


FIG.  300.  —  EARLY  HEROULT  ORE- 
SMELTING   FURNACE. 

The  ore  enters  the  furnace  through  A,  and 
meets  the  coke  which  enters  through  H.  The 
electric  current  enters  at  I,  to  the  positive  elec- 
trode B,  which  is  a  block  of  solid  carbon;  it 
passes  from  B  up  through  the  charge,  being 


on  account  of  its  electrical  resistance,  and  to 
the  negative  electrodes,  F  and  G,  which  are  also 
blocks  of  solid  carbon.  The  negative  electric 
connection  is  a  J.  The  charge  begins  to  become 
heated  at  the  electrodes  F  and  G,  and  con- 
stantly gains  in  temperature  as  it  falls  lower 
and  lower  in  the  furnace. 


THE  ELECTRO-METALLURGY  OF   IRON  AND   STEEL         439 


FIG.   301.  — KELLER   ORE-SMELTING  FURNACE. 

The  two  shafts  are  connected  below  by  means  of  the  channel  AAA.  The  charge,  con- 
sisting of  ore,  coke  and  flux,  enters  the  shafts  at  BB,  BB,  and  passes  downward  in  the  furnace 
as  smelting  progresses.  C  is  the  positive,  and  D  the  negative  electrode,  each  consisting  of 
a  block  of  carbon.  E  and  F  are  also  blocks  of  carbon,  electrically  connected  by  the  cable, 
G.  The  current  enters  at  C  and  passes  through  the  charge  to  E;  thence  it  passes  through 
G  to  F  and  thence  through  the  charge  in  the  other  shaft  to  D.  In  this  way  the  charges  in 
both  shafts  are  heated;  liquid  iron  is  formed  and  collects  in  the  channel,  AAA,  while  the 
slag  floats  on  top  of  it.  When  the  liquid  pool  extends  all  through  AAA  the  current  passes 
through  it  instead  of  through  the  cable  G,  and  thus  the  melted  iron  is  kept  hot.  If  it  should 
become  too  cold,  the  auxiliary  electrode,  H,  is  brought  into  action  and  the  current  enters 
at  this  point  until  the  desired  temperature  is  obtained. 


slag  and,  on  account  of  the   very  high   temperature  available, 
the  slag  is  made  intentionally  very  rich  in  lime,  wherefor  it  has 


440 


THE  METALLURGY   OF   IRON   AND  STEEL 


a  great  solvent  power  for  phosphorus  and  sulphur.  On  this 
account  pig  iron,  very  low  in  these  two  harmful  elements,  can 
be  produced  from  relatively  impure  ores,  and  this  is  one  of  the 
greatest  advantages  of  this  type  of  ore  smelting.  The  pig  iron 
and  slag  are  tapped  from  the  bottom  of  the  furnace  through 
tap  holes,  as  in  other  processes. 

Electric  vs.  Coke  Smelting.  —  The  cost  of  electric  smelting  under 
diverse   conditions   has   been   frequently   estimated   and   figures 


FIG.   302.  — SECTION   OF   KJELLIN   INDUCTION  FURNACE. 

may  be  found  in  several  of  the  references  given  at  the  end  of  this 
chapter.  It  seems  unwise  to  quote  figures  except  where  the  full 
circumstances  and  conditions  are  described,  although  we  may 
estimate  that  the  cost  of  smelting  may  be  as  low  as  $10  per  ton 
of  pig  iron  produced  under  the  most  favorable  circumstances  and 
up  to  $30  per  ton  where  ore  and  water  power  are  not  so  cheap. 


THE   ELECTRO-METALLURGY  OF   IRON  AND   STEEL         441 

The  expense  depends  chiefly  upon  the  cost  for  the  production  of 
electricity,  and  this  is  so  large  that  electric  smelting  is  practically 
never  advisable  except  where  impure  ore  and  water  power  for 


the  production  of  electricity  are  very  cheap,  and  where  pig  iron, 
coke  and  pure  ore  are  expensive.  Besides  the  advantages  of 
being  able  to  produce  a  very  pure  pig  iron  and  to  employ  very 
impure  ores,  we  can  use  electric  smelting  even  where  coke  is  not 
available  by  the  use  of  charcoal  as  a  reducing  agent. 


442  THE  METALLURGY  OF  IRON  AND  STEEL 


ELECTRO-THERMIC  MANUFACTURE  OF  STEEL 

There  are  three  important  types  of  electric  furnace  now  in  use 
for  the  refining  of  pig  iron,  known  respectively  as  the  Kjellin- 
Colby  or  induction  type;  the  Heroult,  and  the  Keller  types. 

Induction  Furnace.  —  The  induction  furnace  is  based  upon 
the  principle  of  the  ordinary  static  transformer,  whereby  alter- 
nating electric  current  is  transformed  to  lower  voltage.  It  was 
independently  developed  by  E.  A.  Colby,  of  the  United  States, 
and  F.  A.  Kjellin,  of  Sweden,  whose  American  rights  have  been 
joined  under  one  management.  A  sectional  elevation  of  the 
furnace  is  shown  in  Fig.  302,  in  which  CCCC  is  the  core  of  an 
electro-magnet,  around  one  leg  of  which  a  coil  of  wire,  AA,  passes. 
When  an  alternating  current  goes  through  the  coil,  A  A,  it  sets 
up  an  alternating  magnetic  field  in  the  core,  CCCC,  and  this  in 
turn  sets  up  a  secondary  current  in  the  circle,  BB,  parallel  to 
the  coil,  A  A.  In  other  words,  an  alternating  current  passing 
through  the  coil,  A  A,  induces  an  alternating  current  in  the  coil, 
BB,  without  there  being  any  metallic  connection  between  the  two. 
This  is  a  well-recognized  phenomenon  in  electrical  engineering 
and  requires  no  further  comment  here.  In  the  furnace  operation, 
the  circle,  BB,  is  a  hollow  ring  in  the  brickwork  into  which  melted 
metal  is  poured.  The  resistance  offered  by  this  melted  metal 
to  the  passage  of  the  induced  current  generates  heat  which  will 
maintain  the  temperature  or  raise  it  to  any  desired  point.  The 
slot,  BB,  is  really  an  annular  crucible  into  which  pig  iron,  steel 
scrap,  iron  ore  and  flux  may  be  charged  as  if  it  were  an  open- 
hearth  furnace,  and  the  operation  of  steel  making  is  practically 
the  same  in  principle  except  that  electric  heat  is  employed  instead 
of  regenerated  gas  and  air.  We  may  charge  solid  metal  if  desired, 
but,  in  such  a  case,  it  is  well  to  leave  a  shallow  circle  of  metal  in 
the  bottom  of  the  slot,  BB,  after  each  operation  is  ended,  to  serve 
to  carry  the  induced  current  during  the  beginning  of  the  next 
operation,  until  the  solid  charge  is  melted. 

There  is  a  tap  hole  for  slag  at  an  upper  level  into  the  slot, 
and  one  or  two  tap  holes  for  metal  at  a  lower  level;  or  sometimes 
the  whole  furnace  is  supported  so  as  to  tip  forward  and  pour  its 
contents  out  of  a  spout.  The  great  advantages  of  the  furnace 
are  the  freedom  of  the  charge  from  contamination  by  impurities 


THE   ELECTRO-METALLURGY   OF   IRON   AND   STEEL        443 

either  in  fuel  or  in  electrodes  or  other  connections,  the  excellent 
control  and  wide  range  of  temperature,  and  the  ease  and  simplicity 


FIG.    304.—  COLBY   FURNACE   POURING. 

of  operation.     Its  disadvantages  are  the  high  cost  for  electricity 
on  account  of  the  low  efficiency  of  the  induction  process,  and 


444 


THE  METALLURGY  OF   IRON  AND  STEEL 


the  expense  for  replacing  the  annular  crucible  when  it  is  badly 
corroded  by  slag  and  oxides.  Indeed,  the  cost  of  this  type  of 
operation  is  so  great  as  to  practically  preclude  it  from  competi- 
tion with  the  open-hearth  process  under  ordinary  circumstances 
and  conditions,  but  it  does  enter  into  direct  competition  with 
the  crucible-steel  process,  because  of  the  purity  obtainable  when 


Longitudinal  Sections-A  B  &-C  D 
FIG.    305  — HEROULT  REFINING   FURNACE. 

pure  charges  are  used,  and  because  of  the  high  cost  of  the  latter 
process  for  crucibles,  labor  and  fuel,  so  that  altogether  more  than 
a  dozen  furnaces  of  the  induction  type  have  been  installed  for 
commercial  production  of  steel  in  Europe,  England  and  America. 
Heroult  Furnace.  —  The  design  and  operation  of  the  Heroult 
steel  furnace  is  even  more  like  an  open-hearth  than  the  induction 


THE  ELECTRO-METALLURGY  OF   IRON  AND   STEEL 


445 


furnace,  although  again  electric  heat  is  substituted  for  regenerated 
gas  and  air.  The  general  form  of  the  furnace  is  shown  in  Figs. 
305  to  306.  There  are  two  electrodes  of  carbon,  one  of  which 
leads  the  current  to  the  charge  and  the  other  conducts  it  away. 
The  electrodes  do  not  touch  the  charge,  but  the  current  arcs 
from  one  electrode  to  the  charge,  through  which  it  passes,  and 
thence  arcs  to  the  negative  electrode.  Thus  combined  arc  and 


Transfers  Section  E  F 
FIG.    306.  —  HEROULT   REFINING   FURNACE. 

resistance  heating  is  used,  and  the  impurities  of  the  electrode 
do  not  come  in  contact  with  the  charge  except  in  so  far  as  the 
electrode  burns  up  and  deposits  its  ash.  When  desired  the 
electrodes  are  lowered  until  they  dip  into  the  slag,  but  never 
touch  the  metal.  The  charges  consist  of  solid  or  liquid  pig  iron, 
steel  scrap  and  flux,  regulated  according  to  the  principle  of  the 
basic  open-hearth  process,  for  the  usual  Heroult  furnace  is  lined 


446  THE  METALLURGY  OF   IRON  AND   STEEL 

with  basic  material.  On  account  of  the  high  temperature  obtain- 
able a  liquid  slag  very  high  in  basic  components  may  be  made, 
and  thus  steel  low  in  phosphorus  and  sulphur  may  be  produced 
from  impure  raw  materials.  The  furnace  is  mounted  so  as  to  tip 
for  discharging  its  contents.  There  are  holes  for  the  admission 
of  air  blast  to  the  interior  of  the  furnace  and  the  operations  of 
adding  ore  and  lime  and  of  working  the  charge  are  similar  to 
those  of  the  basic  open-hearth  process.  There  are  four  Heroult 
steel  furnaces  in  Europe,  and  one  in  the  United  States. 


ELECTROLYTIC  REFINING  OF  IRON 

The  greatest  amount  of  work  on  the  electrolytic  refining  of 
iron  has  been  done  by  C.  F.  Burgess,  of  the  University  of  Wis- 
consin, who  produces  an  iron  that  is  almost  chemically  pure, 
the  chief  foreign  element  being  hydrogen,  whose  presence  renders 
the  metal  very  hard  and  brittle.  The  hydrogen  is  driven  off 
by  heating  the  metal  to  a  high  temperature,  but  this  is  accom- 
plished with  the  result  of  vitiating  the  iron  with  traces  of  carbon 
and  sometimes  other  impurities,  for  iron  has  such  a  great  affinity 
for  carbon  that  it  will  absorb  it  at  a  red  heat  from  coke,  charcoal, 
and  even  from  gases  and  oil  vapors.  Indeed,  if  a  piece  of  electro- 
lytic iron,  or  other  iron  very  low  in  carbon,  be  heated  in  contact 
with  steel  or  wrought  iron  higher  in  carbon,  there  will  be  a  small 
amount  of  transfer  of  carbon  from  the  low-  to  the  high-carbon 
metal.  The  same  difficulty  is  met  with  in  melting  the  metal, 
and  as  its  melting  point  is  1507°  C.  (2745°  F.),  there  are  not 
many  kinds  of  crucibles  that  will  stand  the  heat  necessary  and 
yet  fail  to  yield  carbon,  silicon,  or  some  other  impurity  to  the 
iron.  As  I  understand  it,  it  is  this  difficulty  which  has  been  the 
chief  obstacle  in  the  electrolytic  process,  for  the  electrolysis 
itself  seems  to  be  accomplished  by  Burgess  with  success  and 
economy.  If  the  cost  of  the  electrolytic  product  could  be  brought 
somewhere  near  that  of  Swedish  iron  and  the  other  very  pure 
forms,  it  is  probable  that  it  would  become  a  commercial  commodity 
on  account  of  its  high  magnetic  permeability,  electric  conductility 
and  softness. 

Electrolytic  Process.  —  In  Burgess's  process  the  electrolyte  is 
a  mixture  of  ferrous  sulphate  and  ammonium  sulphate  and  it 


THE   ELECTRO-METALLURGY   OF   IRON  AND   STEEL        447 

is  kept  at  a  temperature  of  30°  C.  (86°  F.).  The  anode  is  ordinary 
wrought  iron  or  steel  and  the  primary  cathode  upon  which  the 
first  metal  is  deposited  is  a  thin  strip  of  sheet  iron.  The  deposited 
metal  sticks  so  slightly  to  this  that  no  difficulty  is  met  with  in 
separating  them  after  the  operation  is  finished.  The  electric  current, 
with  a  density  of  from  6  to  10  amperes  per  square  of  cathode 
surface,  deposits  the  dissolved  iron  upon  the  cathode  with  an 
efficiency  of  nearly  100  per  cent.,  and  cathode  plates  averaging 
about  three  quarters  of  an  inch  thickness  are  produced  in  a 
four  weeks'  run. 

REFERENCES  ON  THE  ELECTRO-METALLURGY  OF 
IRON  AND  STEEL 

171.  Eugene  Haanel,  Superintendent  of  Mines.     "Reports  of  the 

Commission  Appointed  to  Investigate  the  Different  Elec- 
tro-Thermic Processes  for  the  Smelting  of  Iron  Ores  and 
the  Making  of  Steel."  Department  of  the  Interior,  Ottawa, 
Canada,  1904  and  1907. 

172.  A  number  of  valuable  articles  and  references  in  vols.  i  to  v, 

1902  to  1907  inclusive.  The  Electro-Chemical  and  Metal- 
lurgical Industry. 

173.  C.  F.  Burgess  and  Carl  Hambuechen.     "Electrolytic  Iron." 

American  Electro  -  Chemical  Society,  April,  1904.  Ab- 
stracted in  The  Electro  -  Chemical  and  Metallurgical  In- 
dustry, vol.  ii,  1904,  pages  183-185. 

174.  Geo.  P.  Scholl.     "The  Manufacture  of  Ferro-Alloys  in  the 

Electric  Furnace."  The  Electro  -  Chemical  and  Metal- 
lurgical Industry,  vol.  ii,  1904,  pages  349-351,  395-396 
and  449-452. 

175.  A  number  of  valuable  articles  in  W.  Borcher's  Metallurgie, 

vols.  i  to  iv,  1904  to  1907  inclusive. 

176.  Several  valuable  articles  and  abstracts  in  Henry  Le  Chatelier's 

Revue  de  Metallurgie,  vols.  i  to  iv,  1904  to  1907  inclusive. 

177.  John  B.  C.  Kershaw.     "  Electric  Furnace  Methods  of  Iron 

and  Steel  Production,"  vols.  xxxix  and  xl,  The  Iron  Trade 
Review,  1906  and  1907. 

178.  G.  K.  Burgess.     "Melting  Points  of  the  Iron-Group  Ele- 

ments," Reprint  62.  Bureau  of  Standards,  Washington, 
D.  C.  See  this  Bulletin  for  best  references  on  pyrometers. 


XVIII 
THE   METALLOGRAPHY   OF   IRON  AND   STEEL 

METALLOGRAPHY  in  its  larger  sense  is  the  description  or  study 
of  the  structure  of  metals.  That  branch  of  the  subject  which 
comes  under  the  head  of  microscopic  metallography  is,  however, 
the  most  important  because  the  structure  of  most  metals,  espe- 
cially iron  and  steel,  is  discernible  only  when  magnified.  We  shall 
see,  however,  that  the  observation  of  structure  by  eye  —  known  as 
magroscopic  metallography  —  is  not  without  great  value. 

Microscopic  metallography  has  nowr  reached  that  stage  of  im- 
portance where  it  is  viewed  almost  on  a  par  with  chemical  analysis 
and  physical  testing.  In  the  United  States  practically  every 
large  steel  works  is  well  equipped  for  the  microscopic  analysis  of 
its  product,  and,  too,  important  laboratories  of  the  universities  and 
of  consulting  metallurgists  devote  much  attention  to  the  study. 
Although  only  a  little  more  than  twenty  years  have  elapsed  since 
the  art  first  received  public  attention,  it  has  advanced  so  far  as  to 
have  become  by  now  another  and  a  very  serviceable  tool  in  the 
hands  of  the  expert.  I  take  this  opportunity,  however,  of  offering 
a  word  of  warning:  reputations  have  more  than  once  suffered 
severely,  because  of  erroneous  deduction  made  from  microscopic 
evidence,  and  history  has  shown  that  those  who  "rush  in  where 
angels  fear  to  tread  "  are  sure  to  be  caught  sooner  or  later.  The 
wise  man  is  he  who  never  bases  an  opinion  upon  a  sample  whose 
chemical  analysis  is  unknown  to  him:  who  never  bases  an  opinion 
upon  a  microphotographic  negative  or  print,  and  who  polishes 
and  etches  his  own  specimens,  or  has  these  operations  performed 
by  some  one  well  known  to  him  and  working  under  his  immediate 
direction.  With  these  precautions  the  microscope  is  a  very  relia- 
ble index  to  an  experienced  mind. 


448 


THE  METALLOGRAPHY  OF  IRON  AND  STEEL  449 

PREPARATION  OF  SAMPLES  FOR  MICROSCOPIC  EXAMINATION 

Samples  of  iron  and  steel  for  microscopic  analysis  can  be  cut  out 
of  soft  samples  by  means  of  a  hacksaw,  lathe,  or  other  machine, 
and  broken  out  of  hard  and  brittle  samples  by  means  of  a  hammer. 
A  good  rule  to  follow  is  to  have  the  surface  that  is  to  be  polished 
about  f  to  i  of  an  inch  on  a  side.  If  larger  than  that,  it  requires 
excessive  labor  for  polishing.  It  requires  about  sixteen  times  as 
much  labor  to  polish  a  sample  an  inch  square  as  to  polish  one  J 
inch  square,  and  it  requires  about  sixty-four  times  the  labor  to 
polish  one  2  inches  square.  On  the  other  hand  it  is  not  advisable  to 
polish  too  small  an  area,  because  the  surface  will  be  liable  to  con- 
vexity and  therefore  very  difficult  to  get  into  focus,  especially  for 
high  powers. 

Rough  Polishing.  —  After  the  proper  size  of  a  specimen  is  ob- 
tained the  next  step  is  to  give  its  surface  a  bright  mirrorlike  polish, 
free  from  any  scratches  discernible  even  with  high  powers  of  the 
microscope  (1,000  diameters  or  so),  and  this  result  is  achieved 
with  the  greatest  economy  in  labor  by  proceeding  by  gradual 
steps : 

If  the  surface  contains  deep  gouges,  or  marks  produced  by  cut- 
ting or  breaking  it  out,  it  should  first  be  brought  to  a  plane  surface 
by  rubbing  across  a  rough  file,  a  grindstone,  or  an  emery  wheel. 
For  my  own  work  I  much  prefer  to  rub  the  specimen  across  a  file 
rather  tnan  to  put  it  in  a  vice  and  draw  a  file  across  it,  for  I  believe 
the  former  method  produces  a  more  even, — i.e.  less  rounded, — 
surface  and  therefore  conduces  to  economy  of  labor  in  the  later 
operations.  It  is  best  to  hold  the  specimen  lightly  in  the  fingers 
and  draw  it  back  and  forth  across  the  file  in  a  straight  line,  avoiding 
any  circular  motion  and  therefore  having  the  polishing  marks  all 
parallel  and  straight  across,  the  specimen. 

When  a  plane  surface  has  been  produced  in  this  way  the  speci- 
men should  be  rubbed  on  a  very  smooth  file.  In  this  operation 
the  specimen  should  again  be  held  in  the  fingers  and  rubbed  in  a 
straight  line  back  and  forth,  and  should  be  turned  90°  from  the 
first  rubbing  so  that  the  marks  now  made  will  cut  vertically  across 
the  first  scratches.  In  this  way  it  is  very  easy  to  tell  when  the 
scratches  made  by  the  first  file  are  entirely  eliminated  and  the  oper- 
ation on  the  second  file  should  be  continued  to  at  least  this  point 
no  matter  how  short  and  faint  the  old  scratches  may  prove  to  be. 


450  THE  METALLURGY  OF   IRON  AND  STEEL 

It  only  takes  a  minute  or  two  to  remove  the  last  scratches  on  this 
smooth  file,  but  it  would  take  several  minutes  to  remove  them  by 
means  of  one  of  the  later  polishing  mediums,  and  the  greatest 
economy  is  obtained  by  having  each  stage  of  the  operation  abso- 
lutely complete. 

After  coming  off  the  smooth  file,  the  specimen  is  again  turned 
90°,  so  that  the  marks  now  to  be  made  run  in  the  same  direction  as 
those  made  on  the  rough  file,  and  rubbed  across  a  sheet  of  ordinary 
00  emery  paper  cut  to  about  3|  inches  wide  by  9  inches  long  and 
pinned  with  thumb  tacks  upon  a  piece  of  planed,  J-inch  board. 
This  operation  is  continued  until  the  last  marks  from  the  smooth 
file  are  removed. 

Fine  Polishing.  —  The  polishing  then  proceeds  in  the  same 
manner  by  steps  upon  French  emery  paper  of  gradually  increasing 
fineness,  each  piece  being  cut  to  about  3f  inches  by  9  inches  and 
mounted  on  a  smooth  board.  Of  the  Hubert  brand  the  grades  are 
designated  0,  00,  000,  and  0000. 

After  the  0000  French  emery,  the  surface  is  very  smooth  and 
bright  and  is  given  a  final  burnishing  by  rubbing  across  a  piece  of 
broadcloth  or  baize  stretched  over  a  piece  of  wood,  moistened  with 
water  and  covered  with  a  very  thin  liquid  paste  of  water  and  best 
washed  rouge.  This  should  leave  the  specimen  polished  as  bright 
as  a  mirror  and  free  from  all  scratches.  It  may  be,  however,  that 
the  eye  or  a  hand  magnifying  glass  would  discover  microscopic 
rounded  furrows  in  the  specimen.  These  are  due  to  scratches 
made  in  the  early  stages  of  polishing,  which  have  not  been  elimi- 
nated, but  whose  corners  have  been  rounded  off  by  the  finer  grades 
of  polishing  mediums.  I  never  permit  a  specimen  containing  these 
furrows  to  be  used  as  the  basis  of  any  opinion. 

Preparation  of  Rouge.  —  The  best  jeweler's  rouge  purchasable 
is  not  good  enough  for  polishing,  as  it  contains  very  fine  particles  of 
dirt  and  grit  which  produce  scratches  in  the  surface  of  the  specimen 
during  the  final  stages  of  the  process.  It  is  best  washed  by  the 
metallographer  himself.  This  is  best  done  upon  samples  of  not 
more  than  one  teaspoonful  of  rouge  at  a  time  stirred  in  about  a 
glassful  of  water  in  a  flat  pan  or  dish  until  thoroughly  wetted. 
After  allowing  to  settle  for  about  five  minutes  the  wrater  is  poured 
into  an  ordinary  chemist's  wash  bottle  where  it  is  kept  until  ready 
for  use.  The  last  dregs  of  the  water,  containing  a  good  deal  of 
coarse  rouge  and  grit,  is  thrown  away.  A  little  experience  soon 


THE   METALLOGRAPHY  OF   IRON  AND   STEEL  451 

teaches  one  to  get  the  maximum  amount  of  good  rouge  from  a 
sample,  without  any  particles  that  would  produce  scratches.  The 
rouge  in  the  wash  bottle  is  protected  from  dust  and  dirt  and  can  be 
poured  out  of  the  glass  tube  on  to  the  broadcloth  polishing  board 
as  needed.  For  the  preparation  of  special  powders  for  the  very 
finest  grades  of  polishing,  the  reader  is  referred  to  the  references 
at  the  end  of  this  chapter.  I  have  described  here  the  methods 
which  I  prefer  and  use,  but  there  are  many  others  which  are  doubt- 
less equally  as  good. 

Precautions  as  to  Polishing.  —  Do  not  rub  the  specimen  too 
hard  on  the  polishing  mediums.  This  does  not  produce  the  de- 
sired effect  any  more  rapidly  and  may  distort  the  structure  of  the 
metal  so  as  to  lead  to  erroneous  conclusions. 

Do  not  allow  the  specimen  to  become  heated  by  the  polishing. 
This  is  especially  true  of  hardened  steel  and  other  heat-treated 
specimens  which  may  become  tempered  and  so  altered  even  upon 
gentle  heating. 

Rub  a  piece  of  hard  steel  over  each  piece  of  polishing  paper  and 
broadcloth  before  using  it  for  polishing  your  specimen.  This  is 
to  get  rid  of  grit. 

Do  not  lay  polishing  boards  down  where  dust  will  get  on  them, 
but  let  them  stand  with  the  full  height  upward  inside  a  closed  box 
or  a  small  closet. 

Never  form  an  opinion  upon  a  specimen  that  retains  ^scratches 
or  polishing  marks. 

Mechanical  Polishing.  — Instead  of  rubbing  the  specimen  across 
different  mediums  by  hand,  we  can  press  them  against  the  emery 
papers  and  rouge-cloth  mounted  upon  wooden  discs  about  8  inches 
in  diameter,  revolving  at  speeds  of  about  600  r.p.m.  This  method 
saves  time  and  the  necessary  apparatus  is  very  simple  to  make,  or 
can  be  purchased  complete.1  For  my  own  use  I  prefer  hand- 
polishing  except  upon  the  rouge,  because  of  the  liability  to  heating 
the  specimens  with  the  higher  surface-speed,  and  to  damage  of  the 
specimen  by  having  it  snatched  out  of  one's  fingers. 

1  Consult  references  180,  184  and  185,  page  457. 


452  THE  METALLURGY  OF  IRON  AND  STEEL 

DEVELOPING  THE  STRUCTURE  FOR  EXAMINATION 

To  develop  the  structure  of  iron  and  steel  so  as  to  differentiate 
between  the  constituents,  four  methods  are  available : 

(1)  Polishing  in  bas-relief . 

(2)  Etching  with  chemicals. 

(3)  'Polish  attack/ and 

(4)  Heat  tinting. 

Polishing  in  Bas-relief.  —  Where  some  of  the  constituents  are 
less  durable  than  others  the  method  of  polishing  that  I  have  de- 
scribed, upon  a  soft  background,  produces  a  bas-relief,  since  the 
softer  constituents  are  worn  to  a  greater  depth  than  the  harder 
ones.  The  parts  thus  worn  down  appear  darker  than  the  higher 
places  which  reflect  the  light  better.  It  is  by  this  method  that 
graphite  is  best  distinguished  in  pig  iron  and  slag  in  wrought  iron, 
because  the  attack  by  acids  is  liable  to  produce  other  dark  spots 
which  may  not  be  readily  differentiated.  It  is  by  the  bas-relief 
method  that  F.  Osmond  developed  so  beautifully  the  structure  of 
pearlite  shown  in  Fig.  241.  This  method  has  the  disadvantage, 
however,  of  rounding  off  the  edges  of  the  harder  constituents  and 
so  causing  the  softer  ones  to  appear  larger  than  they  really  are. 

Etching  with  Chemicals  —  Nitric  Acid.  —  This  method  is  prob- 
ably the  commonest  one  of  developing  the  structure  of  steel.  Many 
different  strengths  of  acid  are  used  by  different  metallographers 
from  0.1  per  cent,  up  to  20  per  cent.,  and  the  length  of  time  that 
is  necessary  to  expose  the  specimen  will  depend  upon  this  factor 
and  upon  the  amount  of  carbon  present.  High-carbon  steel  will 
require  a  longer  time  than  soft  steel  and  may  take  as  much  as 
2J  minutes,  although  this  is  very  rare.  The  nitric-acid  solutions 
are  usually  made  with  alcohol  instead  of  with  water,  in  order 
to  dry  more  quickly.  Some  metallographers  prefer  to  immerse 
their  specimens  in  the  acid  for  a  given  length  of  time,  and  others 
prefer  to  hold  the  specimen  in  the  hand  with  the  polished  sur- 
face upward,  and  then  deposit  a  few  drops  of  the  etching  fluid 
upon  it  with  a  piece  of  rubber  tubing  on  the  end  of  a  glass  rod. 
In  any  event  it  is  usually  better  to  etch  a  shorter  time  than  is 
estimated  as  suitable,  examine  under  the  microscope,  and  then 
etch  again  if  necessary.  After  every  etching  it  is  necessary 
to  wash  the  specimen  off  with  alcohol  and  dry  as  quickly  as 
possible.  This  drying  is  best  accomplished  by  absorbing  all 


THE  METALLOGRAPHY  OF  IRON  AND  STEEL  453 

the  liquid  left  on  the  surface  after  the  alcohol  wash  with  a  piece 
of  soft  cloth  and  then  holding  in  a  stream  of  air.  Some  metal- 
lographers  wash  the  specimen  after  etching  with  alkali,  and 
then  with  water  and  then  with  alcohol.  Sauveur  immerses  his 
specimen  in  the  strongest  nitric  acid  for  a  few  seconds  and  then 
places  it  in  a  stream  of  running  water,  washes  with  alcohol  and 
dries.  As  the  strong  nitric  acid  puts  the  steel  in  a  passive  state, 
the  length  of  attack  by  this  method  is  only  momentary,  so  that 
it  is  necessary  to  repeat  it  a  few  times.  It  results  in  a  very  even 
etching  of  the  surface. 

Iodine  Etching.  —  Some  investigators  use  iodine  for  etching, 
by  rubbing  a  few  drops  over  the  surface  until  a  film  covers  it,  and 
allowing  it  to  remain  until  the  iodine  color  has  disappeared, 
after  which  the  iodine  is  washed  off  with  alcohol  and  dried.  A 
good  iodine  solution  for  this  purpose  is  the  ordinary  tincture  of 
iodine  diluted  with  an  equal  voluhie  of  alcohol.  It  is  also  well  to 
have  an  auxiliary  solution  of  about  J-  this  strength  for  lighter 
etching  work. 

Picric  Acid  Etching.  —  I  have  found  the  5  per  cent,  of  picric 
acid  in  alcohol,  which  Igevsky  used  for  hardened  and  annealed 
steels,  very  useful  also  for  wrought  iron,  very  low  carbon  steels,  and 
pearlite. 

Polish  Attack.  —  The  method  of  '  polish  attack '  advised  and 
used  by  Osmond,  consists  in  rubbing  the  specimen  upon  a  piece 
of  parchment  stretched  over  a  piece  of  soft  wood  and  moistened 
with  a  2  per  cent,  solution  of  ammonium  nitrate.  This  method 
gives  very  beautiful  results  in  Osmond's  hands  and  is  especially 
valuable  for  developing  the  structure  of  martensite,  troostite, 
pearlite,  and  sorbite. 

Heat  Tinting.  —  Heat  tinting  consists  in 'warming  the  steel 
until  it  becomes  oxidized.  The  different  constituents  are  oxi- 
dized at  a  different  rate  and  so  may  be  distinguished  from  one  an- 
other. It  is  most  serviceable  in  distinguishing  the  phosphide  of 
iron  from  the  carbide,  for  by  heating  until  the  carbide  is  red,  the 
phosphide  (FesP)  will  be  yellow.  The  phosphorus  eutectic  may 
be  distinguished  from  pearlite  in  the  same  way,  because  the  former 
will  be  yellow  when  the  latter  is  blue.  The  heat  tinting  must  be 
accomplished  in  such  a  way  as  not  to  expose  the  metal  directly  to  a 
flame.  The  simplest  method  is  to  put  the  specimen  upon  an  iron 
plate  heated  from  beneath. 


454  THE   METALLURGY  OF   IRON  AND   STEEL 

MICROSCOPE  AND  ACCESSORIES 

It  is  hardly  desirable  to  describe  here  the  different  forms  of 
microscope  and  accessories  used  for  metallographic  work,  as  the 
manipulations  cannot  well  be  learned,  except  by  practice,  and  the 
catalogues  of  the  manufacturers  of  scientific  instruments  of  all 
iron-producing  countries  now  give  full  data.  A  photograph  of  a 
common  illuminating  device,  microscope  and  camera,  is  shown  in 
Fig.  307.  Those  who  expect  to  take  up  the  subject  should  pro- 
cure a  book  upon  it  and  study  it  much  more  fully  than  we  have 
space  for  here.  The  chief  difference  between  the  microscopic  ex- 
amination and  photography  of  iron  and  steel,  and  of  biological 
specimens,  botanical  specimens,  thin  rock  sections,  etc.,  arises 
from  the  non-transparency  of  the  metal.  It  is  necessary  to  illu- 
minate them  from  above,  since  we  cannot  cause  the  light  to  pass 
through  the  specimen  and  into  the  instrument.  This  necessitates 
special  forms  of  illuminators  and  powerful  lights.  For  magnifi- 
cations of  about  500  diameters,  the  Welsbach  mantle  gives  suffi- 
cient illumination.  The  Nernst  lamp  is  also  very  useful,  but  for 
very  high  powers  it  is  necessary  to  use  the  electric  arc  lamp.  This 
introduces  especial  difficulties,  because  the  focus  which  gives  good 
definition  to  the  eye  by  means  of  the  arc  light  will  be  blurred  upon 
the  photographic  plate.  The  use  of  a  light-yellow  screen  in  front 
of  the  light  assists  in  this  difficulty,  but  a  good  deal  of  experience  is 
required  to  get  good  results.  A  mercury  light  avoids  this  difficulty. 

MACROS COPIC  METALLOGRAPHY 

An  experienced  eye  may  get  a  very  good  idea  of  the  size  of 
crystals  in  iron  and  steel  by  examining  a  freshly  broken  fracture, 
and  this  is  one  of  the  branches  of  magroscopic  metallography. 
For  the  most  accurate  results,  however,  it  is  not  as  good  as  mi- 
croscopic examination. 

It  is  also  possible  to  get  other  information  by  etching  a  polished 
surface  for  many  hours  with  dilute  hydrochloric  acid.  For  this 
purpose  the  polishing  need  only  go  as  far  as  the  commercial  00 
emery  paper,  following  the  smoother  file.  In  this  way  the  center 
of  ingots,  because  of  their  looser  texture,  will  be  eaten  away  much 
more  rapidly,  and  this  will  be  evident  to  the  unaided  eye.  Also 
the  interior  of  sections  of  large  area  will  be  attacked  more  than  the 


456 


THE   METALLURGY  OF   IRON   AND   STEEL 


outside,  which  has  become  harder  through  the  work  of  rolling. 
Some  blowholes,  which  cannot  be  seen  by  eye  or  have  been  par- 
tially welded  up,  may  often  be  discovered,  because  the  etching 
action  is  more  severe  in  their  neighborhood,  and  the  same  is  true 


FIGS.  308  TO  311.  — RAILS  ETCHED  FOR  SEVERAL  HOURS  WITH  DILUTE 

HYDROCHLORIC   ACID. 
FIG.  308. —  RAIL  WITH  SOFT  INTERIOR;  ROLLED  FROM  TOO  NEAR 

TOP  OF  INGOT. 
FIG.  309.  —  RAIL  WITH  BLOWHOLES  AND  SOFT  INTERIOR. 


of  spots  where  segregation  has  occurred.  After  etching  and  exam- 
ination, permanent  records  may  be  kept  of  the  indications  by 
covering  the  etched  surface  with  printer's  ink  and  then  pressing  it 
with  a  letter  file  on  to  a  piece  of  cardboard  or  heavy  paper.  A  few 
examples  of  records  made  in  this  way  are  shown  in  Figs.  308 
to  311. 


THE  METALLOGRAPHY  OF   IRON  AND   STEEL  457 

REFERENCES  ON  THE  METALLOGRAPHY  OF  IRON  AND  STEEL 

For  preparation  of  microscopic  specimens: 

180.  W.  Campbell.     "  Notes  on  Metallography."     Columbia  School 

of  Mines  Quarterly,  vol.  xxv,  No.  4  and  vol.  xxvii,  No.  4. 

181.  F.    Osmond   and   J.    E.    Stead.     "Microscopic   Analysis   of 

Metals."     London,  1904. 

182.  Henry  Le  Chatelier.     "  Sur  la  Metallographie  Microscopique." 

Bulletin  de  la  Societe  d' Encouragement  pour  I'lndustrie 
Nationals,  April,  1896.  (In  English,  see)  The  Metallograph- 
ist,  1901,  vol.  iv.  Also:  Congres  International  de  Liege, 
Section  de  Metallurgie,  vol.  i,  pages  255-284. 

183.  E.   Heyn.     See  especially,    Verhandlungen  des   Vereins  zur 

Befoerderung  des  Geiverbfleisses,  1904,  pages  355—397. 
Also:  Stahl  und  Eisen,  vol.  xxvi,  pages  8-16  and  vol. 
xxvi,  pages  580-596. 

184.  J.  E.  Stead.     Journal  of  the  Iron  and  Steel  Institute,  1894, 

No.  1,  page  292;  and  the  Proceedings  of  the  Cleveland  In- 
stitution of  Engineers  (England),  1900. 

185.  The  Metallographist,  vols.  i  to  vi,  1898  to  1903.     Edited  by 

A.  Sauveur,  Boston,  Mass.  Succeeded  by  The  Iron  and 
Steel  Magazine  to  1906. 

186.  Paul  Goerens.     "Einfuhrung  in  die  Metallographie."     Halle 

a.  S.,  1906. 
For  micro-photography: 

187.  Edward  Bausch.     "Manipulation  of  the  Microscope."  Third 

edition.     Rochester,  N.  Y.,  1897. 

188.  Walter  Bagshaw.     "Elementary  Photo-Micrography."  Lon- 

don, 1902. 

189.  Louis  Derr.     "Photography  for  Students  of  Physics  and 

Chemistry."     New  York,  1906. 
1800.  H.  Behrens.     "  Das  Mikroskopische  Gefuege  der  Metalle  und 

Legierungen."     Hamburg,  1894. 
See  also  bibliography  given  at  end  of  No.  116. 


XIX 

CHEMISTRY  AND   PHYSICS  INTRODUCTORY  TO 
METALLURGY 

Chemical  Changes.  —  If  a  piece  of  coal  be  burned,  it  ceases  to 
exist  as  such.  It  disappears  from  sight,  except  for  its  slight  res- 
idue of  ash,  and  apparently  has  been  wiped  out  of  existence  for- 
ever. Likewise,  if  a  piece  of  steel  be  attacked  by  some  acid,  it 
disappears  as  such,  and  only  a  coloration  of  the  acid  gives  evidence 
to  the  eye  of  the  metal  previously  present.  Lastly,  if  a  piece  of 
bright  iron  or  steel  be  exposed  to  the  weather,  it  is  soon  converted 
into  reddish-brown  rust,  which  bears  but  little  resemblance  to  the 
original  metal.  In  the  first  example  the  solid  coal  has  been  com- 
bined with  oxygen  of  the  air  and  converted  to  the  form  of  an 
invisible  gas;  in  the  second  case,  the  iron  has  been  combined  with 
the  acid  and  water  and  converted  into  a  liquid;  in  the  third  case 
the  iron  has  been  combined  with  oxygen  and  converted  into  a 
powder.  In  no  case  has  there  been  any  loss  in  total  amounts  or 
weights,  but  only  a  difference  in  composition  or  substance.  These 
changes  in  composition  are  chemical  changes. 

Physical  Changes.  —  Changes  may  occur  in  form  or  properties 
without  any  change  in  composition:  For  instance,  water  may  be 
converted  into  ice  by  mere  cooling,  and  no  change  in  composition 
will  take  place.  Or  it  may  be  converted  into  steam  by  heating 
and  will  still  be  composed  of  the  same  elemental  constituents  as 
when  it  was  in  the  form  of  ice  or  water.  Iron  may  be  liquid  or 
solid;  it  may  be  cold  or  hot;  it  may  be  magnetic  or  non-magnetic, 
and  all  without  change  in  substance.  These  changes  in  proper- 
ties are  known  as  physical  changes.  They  may  consist  of  changes 
in  form,  strength,  heat,  light,  magnetism,  electricity  —  in  fact, 
everything  but  composition. 

Relation  between  Chemical  and  Physical  Changes.  —  Every 
chemical  change  produces  one  or  more  physical  changes.  Thus, 
chemical  changes  are  always  accompanied  by  a  loss  or  gain  of  heat, 

458 


CHEMISTRY  AND  PHYSICS  459 

and  in  the  examples  cited  in  paragraph  1,  there  were  also  observed 
changes  in  form,  in  color,  etc.  Conversely,  we  shall  see  too  that 
physical  changes  are  often  the  cause  of  starting  chemical  changes: 
heat  is  necessary  to  start  the  chemical  action  of  the  burning  of 
fuel;  pressure  produces  the  explosion  of  dynamite;  electricity 
breaks  up  many  chemical  compounds;  light  produces  the  chemical 
changes  that  make  the  photograph. 

Chemical  Compounds  and  Mechanical  Mixtures.  —  When  coal 
is  burned  it  is  chemically  united  to  the  oxygen  of  the  air,  and  the 
gas  formed  contains  properties  entirely  different  from  anything 
belonging  to  either  of  the  substances  that  compose  it.  Likewise 
when  steel  is  dissolved  in  an  acid,  or  is  converted  to  rust.  This 
is  the  essential  characteristic  of  chemical  action:  that  the  sub- 
stances acting  upon  each  other  lose  their  individual  properties 
and  produce  a  new  substance  with  different  properties.  Not  so 
when  the  substances  are  merely  mixed  together,  no  matter  how 
intimate  that  mixture  may  be.  If  finely  ground  sulphur  be 
mixed  with  finely  ground  iron  no  new  properties  are  produced, 
but  if  the  mixture  be  heated  until  a  chemical  action  takes  place 
and  the  two  substances  unite,  a  new  compound  is  formed,  with 
new  and  different  properties.  Moreover,  once  the  chemical  union 
has  taken  place  the  iron  and  sulphur  cannot  be  separated  except 
by  chemical  means,  whereas  the  mixture  of  the  two  could  be  sep- 
arated by  mechanical  means,  such  as  blowing  the  sulphur  away 
with  a  slow  blast  of  air,  or  picking  up  the  particles  of  iron  with  a 
magnet. 

Chemical  Affinity.  —  The  power  that  causes  substances  to  unite, 
and  that  holds  them  together  afterward  is  known  as  'chem- 
ical affinity.7  Like  gravity,  magnetism  and  some  other  great 
forces,  its  nature  is  not  understood  but  its  influence  is  very  evi- 
dent. Some  substances  have  seemingly  no  affinity  for  each 
other  (for  instance,  mercury  and  iron  will  not  form  a  compound), 
while  others  have  tremendous  affinity  —  such  as  sodium  and 
oxygen,  which  cannot  be  brought  into  each  other's  presence  with- 
out uniting  violently  and  generating  much  heat.  Some  sub- 
stances have  almost  universal  affinities,  like  oxygen  which  unites 
with  every  other  elemental  substance  known  except  one,  while 
others  are  relatively  inert  and  form  few  compounds. 

Conditions  under  which  Chemical  Action  will  Occur.  —  To  start 
chemical  action  it  is  sometimes  only  necessary  to  mix  the  sub- 


460  THE  METALLURGY  OF   IRON  AND  STEEL 

stances,  as,  for  instance,  sodium  and  water;  in  other  cases  we  must 
apply  heat,  or  pressure,  or  electricity,  etc.,  even  though  the  sub- 
stances have  great  affinity  for  each  other  and  unite  vigorously 
after  the  action  is  once  started.  In  other  cases  chemical  action 
is  very  slow,  no  matter  how  started  as,  for  instance,  the  rusting 
of  iron,  the  dissolving  of  rocks  in  water,  etc.  As  a  general  thing 
an  increase  in  temperature  increases  all  chemical  affinities,  but  it 
increases  some  faster  than  others. 

The  Elements.  —  In  the  universe  there  are  millions  of  chemical 
compounds,  and  these  are  mixed  together  to  produce  animal  and 
plant  forms,  the  earth,  sea,  etc.  All  these  compounds  are  different 
combinations  of  only  about  eighty  elemental  substances,  which 
are  known  as  'the  elements/  The  compounds  can  all  be  sep- 
arated into  their  component  parts  by  chemical  means  (perhaps 
aided  by  electricity),  but  the  elements  have  so  far  resisted  every 
attempt  to  break  them  down  into  simpler  substances,  and  they 
are  therefore  considered  as  the  simple  substances  and  the  basis 
of  all  matter.  These  eighty  elemental  substances  are  therefore 
of  great  importance,  but  some  much  more  so  than  others,  for  only 
eleven  of  them  form  the  great  bulk  of  the  earth  as  we  know  it, 
and  the  remainder  are  less  abundant.  The  crust  of  the  earth  is 
made  up  of  the  following  elements: 

Oxygen 47 . 29  per  cent. 

Silicon 27 . 21  per  cent. 

Aluminum 7.81  per  cent. 

Iron 5 . 46  per  cent. 

Calcium 3 . 77  per  cent. 

Magnesium 2 . 68  per  cent. 

Sodium . 2 . 36  per  cent. 

Potassium 2 . 40  per  cent. 

All  others 1 .02  per  cent. 

The  air  is  77  per  cent,  nitrogen  and  23  per  cent,  oxygen. 
Pure  water  is  89  per  cent,  oxygen  and  11  per  cent,  hydrogen. 
Plant  and  animal  forms  are  composed  chiefly  of  combinations  of 
carbon,  hydrogen,  oxygen  and  nitrogen. 

The  air  is  the  only  one  of  the  foregoing  bodies  in  which  the 
elements  are  not  severally  united  in  the  form  of  compounds  of  a 
more  or  less  complicated  nature,  and  it  is  because  the  oxygen  of 
the  air  is  in  the  free,  or  elemental,  state  that  it  is  capable  of  per- 
forming the  chemical  work  of  supporting  life  and  burning  fuels. 

Summary.  —  So  far  we  have  learned  that  the  whole  universe, 


CHEMISTRY  AND   PHYSICS  461 

so  far  as  we  know  it,  is  built  up  of  only  about  eighty  different  sim- 
ple substances,  which  we  call  elements,  and  which  are  sometimes 
mixed  together  and  sometimes  chemically  united,  forming  many 
millions  of  different  combinations.  We  have  also  learned  that  a 
chemical  compound  has  properties  different  from  those  of  any  of 
the  substances  composing  it,  and  that  the  elements  of  the  com- 
pound are  held  together  by  what  is  known  as  '  chemical  affinity.' 
We  have  learned  that  chemical  action  does  not  always  take  place 
when  two  or  more  substances  are  mixed  together,  but  we  have 
often  to  start  it  by  heat,  electricity  or  some  other  means.  Lastly 
we  have  learned  that  all  chemical  action  is  accompanied  either 
by  a  production  or  consumption  of  heat. 

Synthesis.  —  W^hen  two  or  more  elements  are  chemically  united 
to  form  a  compound,  or  when  two  or  more  compounds  are  chem- 
ically united  to  form  a  further  compound,  the  building-up  process 
is  called  a  'synthesis/ 

Analysis.  —  On  the  other  hand,  when  a  compound  is  separated 
into  the  elements  which  compose  it,  the  breaking-down  process 
is  called  an  'analysis';  or,  another  name  for  it  is  a  'decom- 
position/ 

Definition  of  Metallurgy.  —  Metallurgy  is  the  art  of  extracting 
metals  from  their  ores  and  adapting  them  to  their  intended  service. 
As  iron  occurs  in  the  earth  combined  with  one  or  more  other  ele- 
ments, the  process  of  extracting  it  consists  in  decomposing  the 
compounds  and  obtaining  the  metal  from  them.  But  this  is  not 
all  of  the  metallurgy  of  iron  for,  after  it  is  extracted,  it  must  be 
adapted  to  the  service  for  which  it  is  intended,  and  for  this  pur- 
pose various  other  elements  are  combined  with  it  in  proportions 
depending  upon  the  uses  to  which  the  metal  is  to  be  put.  Even 
one  part  of  some  of  the  added  elements  in  ten  thousand  parts  of 
iron  will  make  a  great  difference  in  its  properties,  so  that  these 
syntheses  must  be  performed  with  great  care. 

Qualitative  and  Quantitative  Chemical  Analysis.  —  Chemical 
analysis  is  important  in  metallurgy  in  another  connection,  because 
every  substance  put  into  the  furnaces  for  smelting,  and  every 
substance  produced  must  be  carefully '  analyzed '  in  order  that  we 
may  know  exactly  what  is  in  them  and  guide  our  operations  ac- 
cordingly. A  'qualitative  analysis'  will  show  what  elements  are 
in  any  substance,  while  a  'quantitative  analysis'  will  show  how 
much  of  each  is  present. 


462      THE  METALLURGY  OF  IRON  AND  STEEL 


OXYGEN 

Occurrence.  —  Oxygen  occurs  free  in  the  air;  combined  with 
hydrogen  in  water,  and  combined  with  silicon,  with  metals  and 
with  many  other  elements  in  the  earth's  crust.  It  is  the  most 
abundant  element  known  to  us. 

Uses.  —  When  breathed  into  our  lungs  oxygen  performs  cer- 
tain chemical  reactions  which  produce  the  heat  that  keeps  us 
alive,  and  which  purify  the  blood.  The  only  other  abundant 
constituent , of  the  air  is  nitrogen,  and  this  is  so  inactive  chem- 
ically that  it  serves  chiefly  to  dilute  the  oxygen.  Oxygen  also 
reacts  chemically  with  coal,  coke,  oil,  gas  and  other  fuels  to 
produce  the  heat  for  our  fires,  among  which  we  must  include 
prominently  the  fires  so  necessary  in  metallurgy. 

Preparation.  —  Oxygen  is  very  easily  prepared  in  a  concen- 
trated form  in  a  great  variety  of  ways.  If,  by  means  of  combined 
pressure  and  cold,  air  be  converted  into  a  liquid,  its  two  com- 
ponents may  be  separated  by  centrifugal  force,  or  else  the  nitrogen 
may  be  allowed  to  evaporate,  leaving  the  liquid  oxygen  behind. 
No  chemical  processes  are  necessary  for  this  separation  because 
the  elements  are  not  combined.  Where  a  compound  exists,  other 
means  must  be  employed:  For  example,  water  may.be  decomposed 
into  oxygen  and  hydrogen  by  an  electric  current,  and  from  100 
parts  by  weight  of  water  we  can  always  obtain  89  parts  of  oxygen 
and  11  parts  of  hydrogen,  nothing  being  lost  in  the  change. 

Chemical  Action.  —  Oxygen  is  an  odorless,  colorless,  tasteless 
gas.  At  the  ordinary  temperature  it  forms  few  chemical  reac- 
tions, but,  when  heated,  is  one  of  the  most  active  of  the  elements, 
vigorously  attacking,  for  example,  hydrogen  and  carbon,  as  well 
as  their  mutual  compounds  in  the  form  of  gases,  when  once  a 
chemical  reaction  is  started  with  a  match,  electric  spark  or  similar 
means.  It  also  attacks  almost  all  the  metals  at  a  red  heat,  and 
some  of  them  at  lower  temperatures,  —  iron  for  instance,  which 
is  coated  with  an  '  oxide '  upon  being  heated  about  twice  as  hot 
as  boiling  water.  All  the  simple  compounds  of  the  elements  with 
oxygen  go  under  the  name  of  'oxides/  and  their  formation  is 
accompanied  with  the  production  of  heat. 

Phlogiston  Theory.  —  Centuries  ago  it  was  observed  that  lead, 
when  melted  and  exposed  to  the  air,  became  an  apparently  new 


CHEMISTRY  AND   PHYSICS  463 

substance,  and  at  the  same  time  gained  in  weight.  Starting  with 
the  same  weight  of  lead  and  allowing  the  action  to  go  on  until 
complete,  always  resulted  in  the  same  gain  in  weight.  The  an- 
cients believed  that  this  action  was  the  transfer  from  the  fire  to 
the  metal  of  a  certain  indefinable  substance  which  they  called 
1  phlogiston/  They  learned  that  if  the  lead  and  '  phlogiston '  were 
later  heated  with  charcoal,  metallic  lead  was  again  produced, 
and  they  said  that  the  'phlogiston'  was  driven  out  of  it.  We 
now  know  that  it  was  oxygen  from  the  air  that  attacked  the  lead 
when  melted  and  formed  'lead  oxide/  and  that  when  the  lead 
oxide  was  heated  with  charcoal  (carbon)  the  charcoal  robbed  the 
lead  of  its  oxygen  and  formed  '  carbonic  oxide '  leaving  metallic 
lead  again. 

Oxidation  and  Reduction.  —  When  oxygen  attacks  an  element 
and  forms  an  oxide  the  process  is  said  to  be  an  'oxidation/  and 
when  an  oxide  is  deprived  of  its  oxygen  and  reduced  to  a  metal 
the  process  is  said  to  be  a  'reduction/  Iron  is  'reduced'  from 
its  ores,  which  are  usually  oxides.  Oxidation  and  reduction  are 
therefore  opposite  actions  in  chemistry,  the  first  adding  something 
to  a  substance  and  the  second  taking  something  away.  At  first 
the  terms  were  used  in  connection  with  oxygen  alone,  but  are  now 
applied  to  adding  or  taking  away  anything.  In  metallurgy  oxida- 
tion and  reduction  are  all-important,  for  everything  that  is  re- 
duced goes  with  the  metals,  and  everything  that  is  oxidized  passes 
away  with  the  impurities.  In  the  example  cited  where  melted 
lead  was  oxidized,  the  oxide  separated  itself  from  the  metal  just 
as  fast  as  formed,  floating  upon  the  top  of  it,  and  when  the  reduc- 
tion with  charcoal  was  effected,  the  lead  separated  itself  from  the 
mass  and  dropped  down  into  the  bottom, of  the  furnace  as  fast  as 
it  was  reduced.  This  latter  was  then  a  metallurgical  operation. 

Combustion.  —  Combustion  is  a  form  of  oxidation,  in  which  a 
'  combustible '  is  chemically  united  with  oxygen,  and,  as  we  know, 
this  combustion,  or  burning,  is  our  chief  means  of  obtaining  heat. 
When  there  is  just  the  right  amount  of  both  oxygen  and  com- 
bustible to  enter  into  combination,  we  have  'perfect  combus- 
tion/ but  if  the  compound  is  formed  and  there  is  either  oxygen 
or  combustible  left  over,  we  have 'incomplete  combustion/  In- 
complete combustion  always  means  waste  of  heat.  Thus,  we 
know  that  too  much  air  passed  through  a  fire-bed  will  carry  waste 
heat  up  the  chimney,  or  if  we  have  too  little  oxygen  and  carry  a 


464  THE  METALLURGY  OF   IRON  AND  STEEL 

combustible  gas  up  the  chimney,  or  leave  unburned  fuel  on  the 
grate,  we  again  waste  heat. 

THERMOCHEMISTRY 

Chemical  Energy.  —  If  two  or  more  substances  combine  and 
produce  heat,  they  have  chemical  energy,  and  they  transform 
this  chemical  energy  into  heat  energy,  which  can  be  transformed 
in  turn  into  other  forms  and  into  work.  Not  all  chemical  actions 
produce  heat,  but  some  are  accompanied  by  a  consumption  of 
heat,  and  therefore  use  up  energy,  or  rather,  they  transform  en- 
ergy into  chemical  work.  But  the  heat  energy  so  transformed 
into  chemical  work  is  not  lost,  for  we  can  get  it  back  again  by 
reversing  the  action.  For  instance,  if  lead  oxide  be  reduced,  a 
consumption  of  heat  occurs,  and  the  same  amount  of  heat  will  be 
produced  if  we  burn  the  lead  and  produce  the  oxide  again.  So 
it  is  in  every  case:  the  heat  produced  by  the  formation  of  a  com- 
pound is  the  same  in  amount  as  the  heat  consumed  when  the 
compound  is  broken  up,  and  the  heat  produced  by  any  chemical 
reaction  is  the  same  in  amount  as  that  consumed  when  the  action 
is  reversed.  The  science  that  treats  of  the  heat  changes  accom- 
panying chemical  changes  is  called  'thermo-chemistry.'  As  a 
general  thing  syntheses  and  oxidations  are  accompanied  by  a  pro- 
duction of  heat,  while  decompositions  and  reductions  are  accom- 
panied by  an  absorption  of  heat.  Thermo-chemistry  is  very  im- 
portant in  metallurgy  because  metallurgy  is  chemistry  carried  on 
at  high  temperatures,  and  the  metallurgist  must  know  how  much 
heat  is  required  for  all  his  reactions,  and  by  what  reactions  he  may 
obtain  it. 

Maximum  Affinity.  —  If  iron  is  heated  in  air  the  oxide  of  iron 
is  formed,  and  if  this  be  mixed  with  powdered  aluminum  and  the 
action  started  with  a  fuse,  the  aluminum  will  rob  the  iron  of  its 
oxygen  and  unite  with  it  instead.  The  reason  for  this  is  that 
aluminum  has  a  greater  affinity  for  oxygen  than  iron  has.  This 
process  of  selection  is  a  common^  one  in  chemistry  and  any  sub- 
stance will  decompose  a  compound  provided  it  can  form  a  new 
compound  with  greater  chemical  affinities.  Likewise,  if  we  have 
a  limited  amount  of  a  substance  in  the  presence  of  two  others,  it 
will  combine  with  the  one  for  which  it  has  the  greatest  affinity  to 
the  exclusion  of  the  other.  For  example,  if  we  have  liquid  iron 


CHEMISTRY  AND   PHYSICS  465 

and  aluminum  in  the  presence  of  oxygen,  none  of  the  iron  will  be 
oxidized  until  all  the  aluminum  has  been  oxidized. 

Net  Heat  of  Chemical  Reactions.  —  When  iron  oxide  is  formed, 
195,600  units  of  heat  are  evolved;  when  aluminum  oxide  is  formed, 
392,600  units  of  heat  are  evolved.  Therefore,  when  aluminum 
decomposes  iron  oxide  and  forms  aluminum  oxide  instead,  the 
net  heat  effect  of  the  reaction  is  to  evolve  (392,600-195,600  =  ) 
197,000  units  of  heat.  But  suppose  a  reaction  occurs  in  which 
the  decomposition  brought  about  consumes  more  heat  than  the 
compound  formed  produces?  For  example,  if  iron  oxide  is  at- 
tacked by  carbon  and  deprived  of  its  oxygen  there  will  be  a  net 
loss  of  heat,  instead  of  a  gain,  because  carbonic  oxide  generates 
only  29,160  heat  units  in  its  formation,  while  195,600  heat  units 
are  consumed  in  the  decomposition  of  iron  oxide.  Such  a  reaction 
would  not  go  on  unless  we  constantly  supplied  heat  to  the  bodies. 
This  is  important  in  metallurgy  because  it  means  that  when 
we  smelt  iron  oxide  with  coke  (carbon)  we  cannot  reduce  the 
iron  unless  we  continually  heat  the  bodies.  In  the  case  where 
aluminum  reduced  the  iron  it  was  only  necessary  to  start  the 
reaction,  but  with  carbon  smelting  it  is  not  only  necessary  to 
start  the  action  with  heat,  but  also  to  continually  supply  the 
(195,600-29,160  =  )  166,440  units  of  heat  that  are  absorbed. 

Temperatures.  —  Temperature  is  the  degree  of  heat.  There 
are  two  scales  by  which  it  is  commonly  measured,  known  respec- 
tively as  the  Fahrenheit  and  the  Centigrade  scale.  In  both  of 
these  the  freezing  and  boiling  points  of  water  are  taken  as  the 
standards.  In  the  Fahrenheit  scale,  32°  is  the  freezing  point  of 
water,  and  212°  is  the  boiling  point.  Each  degree  is  therefore 
y^-g-  of  this  interval.  In  the  Centigrade  scale  0°  is  the  freezing 
point  and  100°  is  the  boiling  point  of  water.  Each  degree  is  there- 
fore y^-g-  of  this  interval.  One  degree  Centigrade  equals  1|° 
Fahrenheit.  A  table  of  comparison  is  shown  in  Table  XXXIV, 
page  487. 

Heat  Units.  —  The  amount  of  heat  in  a  body  is  different  from 
its  temperature ;  it  takes  much  more  heat  to  raise  a  pound  of  water 
to  200°  F.  than  it  does  to  raise  a  pound  of  iron,  and  more  to  raise 
iron  than  copper,  lead  or  gold.  There  are  two  standards  by 
which  amounts  of  heat  are  measured:  A  British  Thermal  Unit 
(known  as  B.  T.  U.)  is  the  amount  of  heat  required  to  raise  one 
pound  of  water  one  degree  Fahrenheit;  a  calorie  is  the  amount 


466  THE   METALLURGY   OF   IRON   AND   STEEL 

of  heat  required  to  raise  one  gram  of  water  one  degree  Centigrade. 
In  both  cases  the  water  must  start  at  its  maximum  density,  which 
is  at  39.1°  F.  (  =  4°  C.).  One  B.  T.  U.  equals  252  calories.1  In 
this  book  I  shall  generally  use  calories,  as  that  is  the  ordinary 
system  in  scientific  work.  One  Calorie  =  1,000  calories. 

Summary.  —  We  have  now  learned  that  metallurgy  is  chemis- 
try at  high  temperatures,  and  that  when  iron  is  reduced  from  its 
ores,  we  must  decompose  the  ores,  which  consumes  a  great  deal  of 
heat.  We  have  also  learned  how  heat  is  obtained  from  chemical 
reactions,  and  chiefly  from  combustion.  We  have  learned  that 
oxygen  forms  oxides  with  many  of  the  elements,  and  that  some 
of  the  elements  have  a  greater  affinity  for  oxygen  than  others, 
so  that  they  will  keep,  or  even  take,  the  oxygen  away  from  them. 
Lastly  we  have  learned  that  any  reduced  substances  will  join  with 
the  metal  in  our  furnaces,  and  any  oxidized  ones  will  join  with 
the  impurities,  and  that  the  reduced  substances  will  Jiot  ordinarily 
mix  with  the  oxidized  ones. 

CHEMICAL  EQUATIONS 

Combining  Weights.  —  When  metals  unite  in  compounds  they 
always  do  so  in  certain  definite  porportions.  The  compound  of 
oxygen  and  iron  contains  16  parts  of  oxygen  and  56  of  iron;  that  of 
oxygen  and  calcium,  16  parts  of  oxygen  and  40  of  calcium;  that 
of  iron  and  sulphur,  56  parts  of  iron  and  32  of  sulphur;  that  of 
calcium  and  sulphur,  40  parts  of  calcium  and  32  of  sulphur.  These 
characteristic  combining  weights  are  known  as  ' atomic  weights' 
for  a  reason  that  will  be  evident  shortly.  A  list  of  about  one-half 
of  the  known  elements  with  their  atomic  weights  is  given  in  the 
table  on  the  next  page,  those  which  are  of  the  least  importance 
in  metallurgy  of  iron  and  steel  being  omitted,  and  those  which 
are  of  greatest  importance  being  printed  in  small  capitals. 

The  Atomic  Theory.  —  The  atomic  theory  supposes  that  all  of 
the  elements  are  made  up  of  a  myriad  of  tiny  particles  called  atoms. 
The  atoms  are  the  smallest  particles  of  matter  that  can  exist;  too 
small  to  be  even  conceived  of  by  the  imagination,  and  yet  all 
having  a  definite  size  and  weight  and  incapable  of  being  divided 
into  finer  particles.  All  the  atoms  in  any  one  element  are  alike 
in  composition,  size,  and  weight,  but  differ  in  these  three  proper- 
ties from  the  atoms  of  all  of  the  other  elements.  When  two  or 

1  See  page  171.  One  pound  avoirdupois  =453.59  grams;  one  ounce 
avoirdupois  =28.3495  grams. 


CHEMISTRY   AND   PHYSICS 


467 


TABLE  XXXIII 


MAGNESIUM Mg        24 

MANGANESE Mn        55 

Molybdenum Mo        96 

NICKEL Ni         59 

Nitrogen N         14 

OXYGEN O         16 

PHOSPHORUS P         31 

Potassium K         39 

SILICON Si         28.4 

Silver Ag  108 

Sodium Na        23 

SULPHUR S          32 

Tin Sn  118.5 

Titanium Ti         48 

TUNGSTEN Wo  184 

VANADIUM V         51 

Zinc..  Zn        65.4 


ALUMINUM Al  27 

Antimony Sb  120 

Arsenic As  75 

Barium Ba  137.4 

Bismuth Bi  208 

Boron B  11 

CALCIUM Ca  40 

CARBON C  12 

Chlorine Cl  35.5 

CHROMIUM Cr  52 

Cobalt Co  59 

Copper Cu  63.6 

Fluorine F  19 

Gold Au  197 

HYDROGEN H  1 

Iodine I  127 

IRON Fe  56 

Lead Pb  207 

These  combining  weights  are  used  in  the  laboratories  of  chemical  analysis, 
in  calculating  furnace  burdens  and  similar  work.  A  list  should  be  kept  for 
convenient  reference. 

more  elements  combine  chemically  the  atoms  of  one  are  locked 
with  bonds  of  chemical  affinity  to  the  atoms  of  the  others,  and 
thus  the  weights  of  each  element  entering  the  compound  is  in 
proportion  to  the  weight  of  its  atoms. 

Chemical  Symbols.  —  In  writing  the  elements  it  is  customary 
to  represent  each  by  one  or  two  initial  letters,  instead  of  writing 
the  name  out  in  full.  This  is  a  sort  of  shorthand  of  chemistry. 
The  representative  letters  are  taken  from  the  Latin  name  of  the 
elements,  and  the  same  symbols  are  employed  in  every  civilized 
country  of  the  world.  The  symbol  for  iron  is  Fe,  because  the 
Latin  name  for  iron  is  ferrum.  That  for  aluminum  is  Al;  for  cal- 
cium, Ca;  for  carbon,  C;  for  hydrogen,  H;  for  magnesium,  Mg; 
for  manganese,  Mn;  for  oxygen,  O;  for  phosphorus,  P;  for  silicon, 
Si;  and  for  sulphur,  S.  These  eleven  symbols  should  be  learned, 
as  they  will  be  used  frequently  in  the  body  of  the  work.  Others 
are  shown  in  Table  XXXIII. 

Multiple  Proportions  of  Atomic  Weights.  —  It  does  not  require 
much  thought  to  see  that  atoms  may  combine  in  more  than  one 
way.  For  instance,  one  atom  of  carbon  may  combine  with  one 
atom  of  oxygen,  and  again  one  atom  of  carbon  may  combine  with 
two  atoms  of  oxygen.  In  the  first  compound  there  will  be  12 
weights  of  carbon  and  16  of  oxygen;  in  the  second,  12  weights  of 
carbon  and  32  of  oxygen.  Likewise,  one  atom  of  iron  may  com- 


468  THE  METALLURGY  OF   IRON  AND  STEEL 

bine  with  one  atom  of  oxygen,  or  two  atoms  of  iron  may  combine 
with  three  atoms  of  oxygen.  Each  of  these  compounds  will  have 
different  properties.  It  is  possible  to  represent  these  compounds 
in  a  very  simple  way  by  using  the  symbols  for  the  elements,  for 
each  symbol  designates  one  atom  of  the  element.  To  represent 
the  first  compound  of  carbon  and  oxygen  we  write  their  symbolic 
letters  together  —  thus,  CO.  To  represent  the  compound  con- 
taining one  atom  of  carbon  and  two  of  oxygen  we  write,  COO,  or, 
CO2.  To  represent  the  first  iron  oxide  we  write  —  FeO.  To  rep- 
resent the  second  one,  Fe2O3.  Then  the  formulae  for  these  com- 
pounds tell  us  not  only  what  elements  make  up  the  compound,  but 
also  how  much  of  each  is  present.  For  example,  in  the  first  iron 
oxide  we  have  56  parts  of  iron  and  16  parts  of  oxygen;  in  the  sec- 
ond we  have  112  parts  of  iron  and  48  of  oxygen. 

Molecules.  —  When  two  or  more  atoms  are  held  together  by 
chemical  affinity  the  particle  formed  is  known  as  a.  molecule.  The 
symbol,  CO,  represents  a  molecule  of  carbonic  oxide;  Fe2O3  rep- 
resents a  molecule  of  iron  oxide. 

Chemical  Equations.  —  Chemical  shorthand  may  be  used  to 
represent  chemical  reactions,  and  will  indicate  at  a  glance  what 
is  taking  place.  A  synthesis  will  be  shown  as  follows: 

C       -f        O  CO; 

Carbon  and  oxygen  produce  carbonic  oxide. 

The  decomposition  of  water  would  be  written: 

H2O  2H       +      O; 

Water  gives  hydrogen  and  oxygen. 

The  reduction  of  iron  oxide  by  carbon: 

FeO         +        C  Fe     +  CO; 

Iron  oxide  and  carbon  give  iron  and  carbonic  oxide. 

The  reduction  of  iron  oxide  by  .aluminum: 

Fe2O3       +         2A1          =  2Fe  +  A12O3; 

Iron  oxide  and  aluminum  give  iron  and  aluminum  oxide. 

Indestructibility  of  Matter.  —  In  the  equations  written  above 
it  will  be  noticed  that  there  are  always  as  many  atoms  of  each  ele- 
ment on  the  left-hand  side  of  the  equation  mark  as  on  the  right. 
This  is  in  accordance  with  the  fundamental  law  of  chemistry  that 
matter  can  neither  be  destroyed  nor  created.  If  we  combine  car- 


CHEMISTRY  AND   PHYSICS  469 

bon  with  oxygen  the  weight  of  carbonic  oxide  formed  is  exactly 
equal  to  the  weight  of  carbon  and  oxygen  together.  Also,  if  we 
decompose  water  the  total  weight  of  hydrogen  and  oxygen  will  be 
equal  to  the  weight  of  water  from  which  it  came. 

HYDROGEN 

Occurrence.  —  Hydrogen  forms  11  per  cent,  of  water,  which  is 
a  compound  of  hydrogen  and  oxygen,  whose  molecules  contain 
two  atoms  of  hydrogen  and  one  of  oxygen,  so  that  they  have  the 
formula,  H2O.  Hydrogen  also  occurs  in  all  living  forms. 

Properties.  —  Hydrogen  is  a  colorless,  tasteless,  odorless  gas, 
and  the  lightest  substance  known,  so  that  it  would  be  very  useful 
for  filling  balloons  except  for  its  cost.  It  has  a  high  chemical 
affinity  for  oxygen  and  a  stream  of  it  when  ignited  will  burn  read- 
ily in  the  air  and  produce  water  vapor  with  the  evolution  of  58,060 

calories  : 

2  H  +  O  =  H2O  (+  58,062  cals.). 

It  is  therefore  a  good  combustible,  and  an  impure  form  of  it  is 
indeed  one  of  our  important  fuel  gases,  going  under  the  name  of 
'water  gas/  It  is  also  a  good  'reducing  agent';  that  is,  it  will 
reduce  substances  by  taking  their  oxygen  away. 

Hydrocarbons.  —  Hydrogen  has  a  strong  affinity  for  carbon, 
and  forms  with  it  a  long  series  of  compounds  known  as  'hydro- 
carbons/ of  which  there  are  about  two  hundred  different  com- 
binations. These  form  the  basis  of  mineral  oil,  or  petroleum, 
from  which  we  get  kerosene,  gasoline,  naphtha,  benzene,  lubricating 
oils,  vaseline,  paraffine,  etc.  The  '  light  hydrocarbons  '  are  found 
in  kerosene,  gasoline,  etc.,  while  the  'heavy  hydrocarbons'  are 
found  in  the  less  volatile  oils.  Some  of  the  more  important  com- 
pounds are  as  follows:  Methane,  whose  molecule  has  the  formula, 
CH4,  is  the  chief  constituent  of  natural  gas;  when  it  burns  the  fol- 
lowing reaction  takes  place:  — 


Ethylene,  C2H4,  is  a  heavier  hydrocarbon  than  methane  because 
its  molecule  contains  more  atoms  of  carbon,  while  acetylene, 
C2H2,  is  heavier  still  and  is  the  most  powerful  illuminating  gas 
known.  Benzene,  C6H6,  has  the  same  relation  between  the  atoms 
of  hydrogen  and  carbon  as  acetylene,  but  a  different  number  of 


470  THE  METALLURGY  OF   IRON  AND  STEEL 

t'hem  in  the  molecule,  so  that  it  is  an  entirely  different  substance 
with  different  properties. 

Thermo-chemistry  of  the  Hydrocarbons.  —  When  methane  burns 
we  get  the  following  reaction: — 

CH4+4O  =  2H20       +      CO,.    (+19 1,270  cals.) 
-22,250  cals.+  116,320  cals.  +  97,200  cals. 

If  we  put  the  heat  of  combination  under  each  of  the  compounds 
then  we  can  readily  calculate  the  net  heat  produced  or  consumed 
by  the  reaction,  because  all  the  compounds  on  the  left  of  the 
equation  mark  are  decomposed  and  all  those  on  the  right  are 
formed.  Therefore  the  sum  of  the  heats  on  the  left  is  to  be  com- 
pared with  the  sum  of  the  heats  on  the  right.  If  the  right-hand 
sum  is  greater,  heat  is  produced ;  if  the  left-hand  sum  is  greater, 
heat  is  destroyed.  In  the  burning  of  methane  191,270  calories 
are  produced  and  we  therefore  place  (  +  191,270  cals.)  at  the  end 
of  the  equation. 

Let  us  now  consider  for  comparison  the  reduction  of  tin  oxide 
by  carbonic  oxide,  as  follows : 

SnO2       +       CO     =     SnO      +       CO2  (-2,560  cals.) 
-141,300  cals.  -  29,160  +  70,700  cals.  +  97,200  cals. 

In  this  case  we  find  that  the  sum  on  the  left  is  greater,  and  2,560 
calories  are  consumed.  We  therefore  place  (—2,560  cals.)  next 
to  the  equation. 

Preparation  of  Hydrogen.  —  The  cheapest  method  of  obtaining 
hydrogen  is  by  decomposing  water.  This  may  be  done  as  follows: 

Na    +    H2O  =  H  +  NaOH(+ 33,700  cals.) 
(sodium)  -69,000 '   +  102,700 

We  see  that  this  is  a  heat-producing  reaction.     Another  way: 

C  +  H2O  =  2  H  +  CO  (-28,900  cals.) 
-58,0631      +29,160 

We  do  this  by  passing  water  vapor  over  red-hot  carbon,  but  the 
reaction  consumes  heat  so  we  must  frequently  heat  the  carbon 
or  the  reaction  will  not  go  on. 

Still  another  way  is  to  pass  an  electric  current  through  a  body 
of  water.  Hydrogen  gas  appears  at  one  electric  connection  and 
oxygen  gas  at  the  other.  This  process  is  known  as  the  'electrol- 
ysis' of  water,  and  it  is  an  operation  in  '  electro-chemistry/  If 

1  The  heat  of  formation  of  water  is  69,000  cals.  in  liquid,  form  and  58,060 
in  gaseous  form.  For  other  heats  of  reactions,  see  page  124,  No.  53,  page  125. 


CHEMISTRY  AND  PHYSICS  471 

it  is  carried  out  perfectly  the  amount  of  electric  energy  passed 
into  the  water  will  be  equal  to  the  amount  of  heat  energy  required 
for  the  decomposition,  —  that  is,  69,000  1  calories. 

Summary.  —  Now  we  have  learned  that  each  element  is  con- 
stituted of  infinitesimal  particles  called  atoms  which  are  all  identical 
in  weight  and  composition,  and  that  when  elements  form  com- 
pounds the  atoms  of  one  are  joined  to  those  of  the  other  by  bonds 
of  chemical  affinity.  We  have  also  learned  that  the  atoms  of  ele- 
ments are  represented  by  letter  symbols,  and  that  we  can  express 
reactions  between  them  by  putting  the  symbols  together  in  mole- 
cules and  then  showing  how  they  break  up  and  change  places  to 
form  other  molecules,  and  that  there  are  no  atoms  and  no  weight 
lost  or  gained  in  any  of  these  changes,  but  there  is  a  gain  or  loss 
in  heat  energy  to  correspond  exactly  with  each  loss  or  gain  of 
chemical  energy.  And  we  have  seen  how  the  loss  or  gain  of 
heat  may  be  determined  by  reckoning  the  total  heat  of  com- 
pounds decomposed  as  heat  lost,  and  the  total  heat  of  com- 
pounds formed  as  heat  produced.  From  this  point  we  shall  go 
on  to  consider  the  important  elements  more  in  detail  as  to  their 
chemical  behavior. 

ELEMENTS,  COMPOUNDS,  AND  RADICALS 

Metallic  and  Non-metallic  Elements.  —  All  the  metals  are  ele- 
ments, but  some  of  the  elements  are  not  metals;  for  instance,  we 
know  without  being  told  that  oxygen  is  not  a  metal.  The  dis- 
tinction between  metallic  and  non-metallic  elements  is  not  very 
clear.  It  once  was  considered  that  all  elements  which  looked  like 
metals  should  be  classified  as  such;  they  were  said  to  have  'me- 
tallic luster/  And  all  others  were  classified  as  non-metals.  But 
this  classification  has  been  shown  to  be  deceiving,  and  a  chemical 
one  has  taken  its  place :  Now  all  the  elements  that  form  '  bases ' 
are  classified  as  metals,  and  all  those  that  form  '  acids '  are  classi- 
fied as  non-metals. 

Acids  and  Bases.  —  Acids  are  generally  sharp  to  the  taste  and 
have  certain  other  characteristic  chemical  properties  of  which  one 
of  the  most  distinctive  is  their  ability  to  turn  litmus  a  red  color. 
Bases  have  certain  other  characteristic  properties  of  which  one 
of  the  most  distinctive  is  their  ability  to  turn  litmus  a  blue  color. 
1  See  footnote,  page  470. 


472  THE  METALLURGY  OF  IRON  AND  STEEL 

Acids  will  destroy  the  characteristic  properties  of  bases  and  neu- 
tralize them,  and  conversely,  bases  will  neutralize  acids.  Acids 
and  bases  have  strong  affinity  for  each  other  and  either  one  will 
attack  the  other  if  opportunity  offers.  That  is  why  a  basic  slag 
will  attack  an  acid  furnace  lining,  or  an  acid  slag  will  attack  a 
basic  lining.  Metallurgical  acids  are  '  anhydrous  '  (water-free). 

Salts.  —  When  an  acid  and  a  base  just  neutralize  each  other 
they  form  what  is  known  as  a  salt.  Let  us  dissolve  36.5  grains  of 
hydrochloric  acid,  HC1,  in  water,  and  put  a  piece  of  paper  soaked 
in  litmus  in  it;  the  paper  will  at  once  turn  a  brilliant  red.  Now 
let  us  dissolve  40  grains  of  caustic  soda,  NaOH,  in  another  vessel. 
Caustic  soda  is  a  strong  base ;  if  we  put  one  end  of  our  piece  of  red 
litmus  paper  in  the  solution  it  will  turn  blue.  Now  let  us  pour 
the  acid  solution  into  the  basic  solution,  and  we  will  get  the 
following  reaction: — 

HC1  +  NaOH  =  NAC1  +  H2O. 
36.5         40          58.5        18 

Now,  36.5  is  the  molecular  weight  of  HC1  (because  one  atom  of 
hydrogen  weighs  1,  and  one  of  chlorine  weighs  35.5),  and  40  is  the 
molecular  weight  of  NaOH  (one  atom  of  Na=23;  one  of  O  =  16, 
and  one  of  H  =  1) ;  therefore  there  must  be  as  many  molecules  of 
HC1  present  as  of  NaOH,  and  a  complete  neutralization  will  occur. 
Moreover  it  will  be  seen  that  the  total  weight  of  atoms  at  the  right 
of  the  equation  mark  is  the  same  as  that  at  the  left.  This  neu- 
tralization forms  •  '  sodium  chloride/  which  is  our  common  table 
salt.  The  salt  will  be  dissolved  in  the  water  used  in  the  experi- 
ment. If  now  we  put  in  this  salt  solution  the  piece  of  litmus 
paper,  one  end  of  which  is  red  and  the  other  blue,  it  will  not 
change  its  colors  at  all. 

Radicals.  —  Let  us  consider  the  neutralization  of  caustic  soda 
by  sulphuric  acid,  H2S04*. 

2NaOH  +  H2SO4  =  Na2SO4  +  2H2O. 
80  98  142  36 

In  this  reaction  the  S04  has  changed  places  with  the  OH.  When 
two  or  more  atoms  are  joined  together  and  travel  around  in  com- 
pany in  this  way,  acting  as  if  they  were  inseparable,  they  are 
called  'radicals/  In  this  reaction,  the  S04  is  called  an  'acid 
radical/  and  the  OH  is  called  the  'hydroxide  radical.'  For  the 
time  being  these  radicals  act  as  if  they  were  elementary  substances. 


CHEMISTRY  AND  PHYSICS  473 

Valence.  —  Let  us  consider  four  compounds  with  hydrogen, 

as  follows: 

C1H  OH2         NH3  CH4 

Hydrochloric  acid,     water,     ammonia,     methane. 

One  atom  of  hydrogen  can  hold  one  of  chlorine,  but  it  takes  two 
to  hold  one  atom  of  oxygen,  three  to  hold  one  of  nitrogen,  and 
four  to  hold  one  of  carbon.  Conversely,  one  of  chlorine  can  hold 
one  of  hydrogen,  one  of  oxygen  can  hold  two  of  hydrogen,  one  of 
nitrogen,  three,  and  one  of  carbon,  four.  This  capacity  for  hold- 
ing numbers  of  atoms  is  called  'valence/  In  the  compounds 
shown  above,  chlorine  is  uni-valent,  oxygen  is  bi-valent,  nitrogen, 
tri-valent,  and  carbon,  quadri-valent.  In  each  case  hydrogen  is 
uni-valent;  indeed  hydrogen  is  established  as  the  standard  of 
valency,  with  a  holding  power  of  one.  We  can  determine  the 
valence  of  other  elements  by  learning  how  many  atoms  of  hydro- 
gen they  will  hold,  or,  if  they  do  not  form  a  compound  with  hy- 
drogen, we  can  compare  them  with  some  other  element  that  does. 
For  example,  calcium  forms  a  very  common  oxide,  CaO,  known 
as  lime.  In  lime  calcium  holds  one  atom  of  oxygen;  but  it  takes 
two  atoms  of  hydrogen  to  hold  one  atom  of  oxygen ;  therefore  cal- 
cium is  bi-valent. 

Chemical  Stability.  —  We  have  already  seen  enough  com- 
pounds to  know  that  the  valence  of  several  of  the  elements  is  not 
a  constant  quantity.  For  example,  carbon  and  hydrogen  atoms 
unite  in  nearly  two  hundred  different  combinations.  Likewise, 
iron  forms  FeO  and  Fe203.  In  the  first  it  has  a  valence  of  two; 
in  the  second,  of  three.  But  there  is  a  difference  in  the  stability 
of  these  compounds;  the  oxide,  FeO,  can  only  exist  under  strong 
reducing  conditions,  and  will  take  on  more  oxygen  with  the  least 
opportunity.  Iron  forms  two  sulphides,  designated  as  FeS  and 
FeS2.  In  the  second  compound  it  has  a  valence  of  four,  but  this 
sulphide  is  not  as  strong  a  one  as  the  other,  and  the  second  atom 
of  sulphur  may  be  driven  off  by  heating  it  slightly:  FeS2  =  FeS  +  S. 

Ferrous  and  Ferric  Compounds.  —  The  oxide,  FeO,  is  called 
' ferrous  oxide';  while  FeS  is  called  ' ferrous  sulphide.'  The  ox- 
ide, Fe203,  is  called  'ferric  oxide/  while  FeS2  is  called  'ferric  sul- 
phide/ Manganese  forms  two  oxides:  MnO  is  called  'manga- 
nous  oxide/  and  Mn02  is  called  'manganic  oxide.'  So  with  all 
compounds;  that  having  the  lower  valence  is  given  the  suffix 
-ous,  and  that  with  the  higher  valence,  -ic. 


474  THE  METALLURGY  OF   IRON  AND  STEEL 

Mono-,  Bi-,  Tri-,  etc.  —  FeS  is  also  called  '  iron  mono-sul- 
phide/ from  the  Latin,  meaning  one;  FeS>2  is  sometimes  called 
'iron  bi-sulphide.'  MnO  is  called  'manganese  monoxide/  and 
MnO2,  '  manganese  bi-oxide  '  (di-oxide  is  sometimes  used  instead 
of  bi-oxide).  H20  is  'hydrogen  monoxide';  H2O2  is  'hydrogen 
di-oxide.  '  Fe20s  is  called  'iron  sesqui-oxide/  from  the  Latin 
meaning  three  halves. 

Sub-  and  Per-.  —  When  an  element  has  a  very  low  valence 
it  is  given  the  prefix  'sub-/  and  when  it  has  an  unusually  high 
valence  it  has  the  prefix  'per-.'  For  example,  Fe2O  (if  such  a 
compound  were  capable  of  forming)  would  be  called  'iron  sub- 
oxide';  while  FeO2  (if  possible)  would  be  called  'iron  peroxide.' 
H2O2  is  often  known  as  'hydrogen  per-oxide.'  In  the  same  way 
we  may  have  sub-sulphides  (Fe7S8  is  called  '  iron  sub-sulphide  ')  , 
sub-carbides,  etc. 

Oxidizing  Agents.  —  When  additional  atoms  are  put  in  the 
molecules  of  a  compound  it  is  said  to  be  oxidized.  For  example, 
FeO  will  be  oxidized  to  Fe2O3  (2  FeO  +  O  =  Fe203)  ;  FeS  will  be 
oxidized  to  FeS^  Oxidation  can  only  be  produced  by  means 
of  some  'oxidizing  agent.'  The  commonest  oxidizing  agent  in 
metallurgy  is  the  oxygen  of  the  air,  and  the  next  most  important 
in  iron  and  steel  processes  is  Fe2O3,  and  slags  very  rich  in  Fe2O3: 

3  Si  +  2  Fe2O3  =  3  SiOa  +   4  Fe 
6  P  +  5  Fe2O3  -  3  P2O5  +  10  Fe 

Another  important  one  is  carbon  di-oxide  : 


Redwing  Agents.  —  When  atoms  are  taken  out  of  the  mole- 
cule of  a  compound  it  is  said  to  be  reduced.  Reduction  can  only 
go  on  in  the  presence  of  some  '  reducing  agent/  The  commonest 
reducing  agent  in  metallurgy  is  carbon  in  the  form  of  coke,  char- 
coal, etc. 


Another  one  is  carbon  monoxide,  and  another  is  hydrogen: 


Manganese  is  also  a  reducing  agent  for  iron: 

=  Fe  +  MnO. 


CHEMISTRY  AND   PHYSICS  475 

CHEMICAL  REACTIONS  AND  COMPOUNDS 

Organic  and  Inorganic  Chemistry.  —  The  chemistry  of  living 
organisms,  such  as  plants,  animals,  etc.,  is  a  very  complex  sub- 
ject, and  quite  distinct  from  inorganic  chemistry.  Because  car- 
bon enters  into  all  organisms  we  may  describe  organic  chemistry 
as  the  chemistry  of  the  carbon  compounds.  Inorganic  chemistry 
is  the  chemistry  of  the  metals  and  of  compounds  in  which  carbon 
enters  in  relatively  small  proportions.  Inorganic  chemistry  is 
the  only  one  that  concerns  metallurgists  especially. 

Wet  and  Dry  Chemistry.  —  In  the  analytical  laboratories  they 
perform  their  chemical  reactions  by  dissolving  everything  in 
water  and  so  getting  them  in  the  liquid  form,  because  solids  do  not 
unite  with  each  other  rapidly,  and  gases  are  not  easily  controlled. 
This  branch  of  chemistry  is  known  as  'wet  chemistry/  In  iron 
and  steel  metallurgy,  however,  we  get  everything  in  liquid  form  by 
melting  it.  This  is  known  as  'dry  chemistry/  The  reactions  that 
take  place  in  dry  chemistry  are  the  same  in  principle  as  those  of 
wet  chemistry.  The  chief  difference  is  that  we  cause  substances 
to  react  directly  instead  of  dissolving  them  all  in  water. 

Carbon.  —  Carbon  occurs  in  the  earth  in  the  crystallized  form 
as  graphite  and  as  diamonds.  Of  these  the  diamond  is  the  purer 
variety,  but  both  may  be  considered  as  pure  carbon  in  different 
forms.  The  element  may  be  obtained  in  a  massive,  or  uncrys- 
tallized,  form  by  burning  organic  matter,  such  as  wood,  when  a 
black  residue  of  carbon  (charcoal)  will  be  left.  The  most  abundant 
occurrence  of  carbon  is,  however,  in  combination  with  other  ele- 
ments in  the  various  forms  of  living  matter,  and  also  in  inorganic 
compounds  with  metals,  known  as  carbonates,  such  as  the  car- 
bonate of  lime,  CaCOs,  called  limestone,  or,  when  in  the  crystallized 
form,  marble. 

When  bituminous  coal  is  burned  in  a  smothered  sort  of  way, 
that  is,  in  the  absence  of  much  air,  a  silvery-gray  residue  is  left 
which  is  an  impure  form  of  carbon,  called  coke.  Crystals  of 
graphite  often  are  present  on  the  surface  of  coke.  This  coke  is 
one  of  the  most  important  of  all  metallurgical  reducing  agents, 
as  well  as  fuels,  Carbon  also  forms  a  number  of  hydro-car- 
bons which  are  used  in  the  form  of  gases  as  reducing  agents  and 
fuels,  because  both  their  carbon  and  hydrogen  will  unite  with 
oxygen. 


476  THE   METALLURGY  OF   IRON  AND   STEEL 

Carbon  forms  two  oxides,  —  CO  and  C02.  The  first  combina- 
tion is  accompanied  with  the  production  of  29,160  calories,  and 
the  second,  97,200  calories.  The  formation  of  CO  is  not  complete 
combustion,  because  it  will  itself  be  further  oxidized :  CO  +  O  =  C02, 
with  the  evolution  of  68,040  calories.  The  heat  of  formation  of 
C  +  O  together  with  that  of  CO  +  O  is  just  equal  to  that  of  the 

reaction : 

C  +  2  O  =  CO2  (+  97,200  cals.) ; 
29,160  +  68,040  =  97,200. 

Carbon  di-oxide,  CO2,  is  an  acid  radical  and  unites  with  many 
bases  to  form  'carbonates/  of  which  the  commonest  are  those 
of  calcium,  CaCO3,  magnesium,  MgCO3,  and  sodium,  Na2CO3. 
As  CO2  is  very  volatile,  the  carbonates  may  be  decomposed  by 
heat,  which  drives  the  CO2  off  as  a  gas: 

Na2CO3  =  Na2O  +  CO2. 

Chemical  Behavior  of  Iron.  —  Iron  is  attacked  by  many  of 
the  wet  acids,  —  sulphuric,  nitric,  hydrochloric,  acetic,  etc. 
When  heated  it  is  attacked  by  oxygen,  and  also  when  cold  pro- 
vided the  air  is  damp.  At  a  red  heat,  iron  decomposes  water 
vapor  (2Fe  +  3H2O  =  Fe2O3  +  6H).  It  has  a  high  affinity  for 
oxygen,  and  also  for  small  amounts  of  carbon,  silicon,  sulphur, 
phosphorus  and  hydrogen.  The  last-named  gas  will  penetrate 
solid  iron  very  readily  at  a  red  heat  and  form  a  compound  with  it. 
Iron  practically  never  occurs  in  the  earth  except  combined  with 
oxygen  or  some  other  elements. 

Chemical  Behavior  of  Silicon.  —  Silicon  has  a  high  affinity  for 
oxygen,  with  which  it  forms  a  very  common  oxide,  SiO2,  which 
is  known  as  silica.  This  compound  is  decomposed  with  great 
difficulty;  the  following  reaction  takes  place  only  when  we  get 
to  the  very  high  temperature  in  the  hearth  of  the  iron  blast  fur- 
nace : 

SiO2  +  2C  =  Si +  2  CO  (-121,680  cals.) 
-  180,000  +  2  X  29, 160  =  58,320. 

We  must  remember  the  difference  between  silicon  and  its  oxide, 
silica.  Silicon  never  occurs  uncombined  in  the  earth,  but  silica 
is  the  most  abundant  constituent  known  to  us.  Quartz  is  a  crys- 
tallized form  of  pure  silica,  while  flint,  jasper,  agate,  etc.,  are 
uncrystallized  forms.  Opal  is  silica  combined  with  water. 


CHEMISTRY  AND   PHYSICS  477 

Silicates.  —  Silica  is  the  great  acid  of  dry  chemistry,  and  when 
in  the  melted  condition  will  neutralize  every  base  with  which  it 
comes  in  contact,  forming  a  series  of  salts  known  as  '  silicates.' 
The  great  bulk  of  the  earth's  rocks  are  either  pure  silica  or  silicates 
of  the  different  metals,  and  all  metallurgical  slags  are  silicates. 
The  mono-silicate  of  iron  has  the  formula,  —  Fe2SiO4.  But  it  is 
more  commonly  written,  —  (FeO)2Si02,  which  is  the  same  as 
Fe2O2Si02.  The  series  of  commonest  iron  silicates  are  given 

below: 

FeO.SiO*  Sub-silicate. 
(FeO)^SiOa  Mono-silicate. 
(FeO)2(SiO2)3  Sesqui-silicate. 
FeO(SiO2)2  Bi-silicate. 
FeO(SiO2)3  Tri -silicate. 

With  lime,  CaO,  and  magnesia,  MgO,  a  similar  series  is  formed, 
but  the  silicates  of  alumina,  A1203,  are  more  complicated  in  com- 
position. The  different  metallic  silicates  have  the  property  of 
dissolving  in  each  other  when  melted,  and  of  dissolving  the  oxides 
of  metals,  and  various  other  oxidized  substances,  but  not  of  dis- 
solving metals  or  reduced  substances. 

Feldspar.  —  With  potassium  and  aluminum  silica  forms  a 
series  of  silicates  known  as  the  feldspars,  which  are  common  con- 
stituents of  the  earth's  crust.  The  feldspars  are  chiefly  important 
because  when  reduced  to  powdered  form  they  become  clay,  which 
has  the  peculiar  property  of  becoming  plastic  when  moistened. 
The  purer  clays  melt  at  a  very  high  temperature  and  are  therefore 
used  as  the  bond  to  hold  together  the  material  for  the  linings  of 
furnaces,  but  the  clays  that  contain  much  potassium  or  sodium 
melt  relatively  easily,  and  are  not  so  '  refractory.'  Clays  contain 
a  certain  amount  of  water  of  crystallization,  that  is,  water  chem- 
ically combined  with  the  molecule  of  the  silicates.  If  they  are 
heated  so  hot  that  this  water  of  crystallization  is  driven  out  of 
them,  they  will  not  again  become  plastic. 

Chemical  Behavior  of  Aluminum.  —  Aluminum  has  great  affin- 
ity for  oxygen  and  is  therefore  used,  like  silicon,  for  the  purpose 
of  de-oxidizing  steel: 

3  FeO  +  2  Al  =  3  Fe  +  A12O3. 

Indeed  aluminum  retains  its  oxygen  more  tenaciously  than  silicon, 
and  even  the  highest  temperature  of  our  fuel  furnaces  does  not 


478  THE  METALLURGY  OF   IRON   AND   STEEL 

effect  its  reduction.  The  oxide  of  aluminum,  A12O3,  called  alu- 
mina, is  a  common  constituent  of  rocks,  and  when  nearly  pure  is 
used  as  an  ore  of  the  metal,  its  reduction  being  effected  in  electric 
furnaces.  Alumina  is  very  refractory,  that  is,  it  will  stand  a  high 
temperature  without  melting,  and  is  neutral  in  character,  that  is, 
it  is  attacked  neither  by  acid  nor  basic  slags.  It  is  therefore  used 
as  a  neutral  lining  for  some  furnaces.  Alumina  is  also  useful  in 
blast-furnace  slags;  in  acid  slags  it  acts  as  a  base,  and  in  basic 
slags  as  an  acid,  rendering  the  slags  more  fluid. 

Chemical  Behavior  of  Manganese.  —  Manganese  has  a  higher 
affinity  for  both  oxygen  and  sulphur  than  iron  has,  and  is  there- 
fore used  as  a  de-oxidizer  and  de-sulphurizer  of  iron  and  steel.  If 
sufficient  manganese  is  present,  and  the  metal  bath  kept  liquid  a 
sufficient  time,  neither  oxygen  nor  sulphur  will  be  found  com- 
bined with  iron: 

* 

n  =  MnO+Fe; 
n  =  MnS+Fe. 

Chemical  Behavior  of  Sulphur.  —  Sulphur  is  found  in  the  earth 
native  (that  is,  free  from  combination),  especially  in  volcanic  re- 
gions, and  also  combined  with  metals  as  sulphides.  Iron  bi- 
sulphide, called  'iron  pyrites/  FeS^  is  very  abundant  and  is  the 
chief  source  of  sulphuric  acid  manufacture,  while  the  sulphides 
of  copper,  lead,  and  zinc  are  the  principal  commercial  ores  of 
those  metals.  Iron  sulphides  are  not  used  so  much  as  ores  on 
account  of  the  expense  of  ridding  the  iron  of  sulphur,  which  is 
very  harmful  to  it.  Sulphur  readily  combines  with  oxygen  at  a 
slightly  elevated  temperature  to  form  S02  and  SOs,  and  these  com- 
bine with  water  to  form  sulphurous  and  sulphuric  acids  (H2O-f 
SO2  =  H2SO3;  and  H2O  +  SO3  =  H2SO4) .  In  wet  chemistry  sul- 
phuric acid  attacks  metals  to  form  sulphates: 

2Fe  +  3H2SO4  =  6  H  +  Fe2SsO12  or  Fe2(SO4)3. 
Ca  +  H2SO4  =  2  H  +  CaSO4. 

Phosphorus.  —  Phosphorus  occurs  in  nature  usually  as  metallic 
phosphates,  and  chiefly  as  phosphate  of  lime,  Ca2(PO4)2,  a  natural 
mineral  to  which  the  name  of  apatite  is  given.  It  is  in  this  form 
that  it  ordinarily  gets  into  the  blast  furnace  with  the  iron  ores 
which  it  accompanies  in  the  earth.  Phosphate  is  necessary  to 
animal  and  vegetable  life  and  a  good  part  of  bones  and  living 


CHEMISTRY  AND  PHYSICS  479 

organisms  are  composed  of  it.  The  phosphates  that  will  dissolve 
easily  are  therefore  valuable  fertilizers.  Consequently  certain 
slags  which  are  used  to  remove  the  phosphorus  from  steel  can  be 
sold  for  fertilizing  purposes. 

Phosphorus  acts  the  part  of  an  acid-forming  element,  and  the 
phosphate  radical  will  form  salts  with  many  metallic  oxides,  but 
especially  with  iron  oxides,  magnesium  oxide  and  lime,  for  the 
latter  of  which  it  has  great  affinity.  But  it  is  a  weaker  acid 
than  silica,  and  silica  will  drive  the  phosphate  radical  away  from 
all  the  basic  radicals  until  the  silica  has  completely  satisfied  itself. 
For  this  reason  phosphorus  cannot  be  combined  in  slags  unless 
there  is  a  superfluity  of  bases  present  over  the  amount  necessary 
to  practically  surfeit  the  silica.  In  our  iron  slags  this  means 
usually  at  least  40  per  cent,  of  lime  plus  magnesia  plus  iron  oxide. 

Calcium  and  Magnesium.  —  Calcium  forms  a  very  common 
oxide,  CaO,  known  as  lime,  and  magnesia  forms  a  similar  one, 
MgO,  called  magnesia.  These  occur  in  nature  chiefly  combined 
with  carbonic  acid  to  form  carbonates;  CaCOa  is  called  limestone, 
and  MgCOs,  magnesite.  The  two  carbonates  often  occur  com- 
bined together  in  a  compound  having  the  formula,  —  (Ca.MgJCOs. 
This  type  of  formula  is  used  to  indicate  that  the  calcium  and 
magnesium  replace  each  other  in  the  carbonate  in  almost  any 
relative  proportion.  The  natural  rock,  (Ca.Mg)CO3  has  the  miner- 
alogical  name  of  '  dolomite/ 

Limestone  is  used  as  a  material  to  add  to  the  charge  of  the 
iron  blast  furnace  because  the  carbonic  acid  is  driven  off  in  the 
upper  levels  of  the  furnace  as  soon  as  it  begins  to  become  hot 
(CaCOs  +  heat  =  CaO  +  C02)  and  the  lime  so  produced  serves  as  a 
base  in  the  blast-furnace  slag.  Burnt  limestone,  that  is,  limestone 
from  which  the  carbonic  acid  has  been  driven  off  by  heat,  is  also 
added  to  the  slags  made  in  some  of  the  steel  furnaces,  in  order  to 
increase  their  basicity.  Lime  has  the  peculiarity  of  absorbing 
moisture  from  the  air  and  forming  a  hydrate  [CaO  +  H2O  = 
Ca(OH)2].  This  is  known  as  'slacking/  and  it  causes  the  lime 
to  lose  its  coherence.  For  this  reason  furnace  linings  cannot  be 
made  of  it. 

Magnesia  is  made  by  burning  magnesite  (MgCOa  + heat = MgO 
+  C02),  and  this  is  much  used  for  making  the  basic  linings  of 
furnaces.  Burnt  dolomite  is  used  for  patching  basic  furnace  lin- 
ings, but  it  is  not  as  durable  as  magnesia  for  the  original  lining. 


480  THE  METALLURGY  OF   IRON  AND  STEEL 


CHEMICAL  SOLUTIONS 

Chemical  Compounds,  Mechanical  Mixtures,  and  Chemical 
Solutions.  —  We  have  learned  that  the  differences  between  me- 
chanical mixtures  and  chemical  compounds  are:  (1)  The  proper- 
ties of  compounds  are  different  from  those  of  its  components ;  (2) 
the  formation  of  a  compound  is  attended  with  the  production 
of  heat ;  (3)  the  components  of  a  compound  are  held  together  with 
bonds  of  chemical  affinity,  and  (4)  the  components  always  form 
the  compound  in  the  same  definite  proportions.  There  is  another 
class  of  combinations  different  from  both  compounds  and  mix- 
tures, and  known  as  solutions.  These  have  some  of  the  charac- 
teristics of  compounds  and  also  of  mixtures.  (1)  The  properties 
of  a  solution  are  different  from  those  of  its  components,  but  not 
to  as  marked  a  degree  as  is  the  case  with  compounds;  (2)  its  for- 
mation is  attended  with  the  production  or  consumption  of  heat; 
(3)  the  components  of  the  solution  are  held  together  by  bonds  of 
chemical  affinity,  and  can  only  be  separated  by  chemical  means, 
or  by  electricity,  but  (4)  unlike  compounds,  and  to  a  limited  de- 
gree like  mixtures,  the  components  of  a  solution  may  vary  widely 
in  proportions.  In  some  cases  the  variation  is  infinite,  as  with 
melted  gold  and  silver,  which  will  dissolve  in  each  other  in  any 
proportion;  likewise,  with  melted  copper  and  silver.  In  other 
cases  the  limit  of  solubility  is  very  narrow,  as  in  the  case  of 
melted  iron,  which  will  dissolve  only  about  5  per  cent,  of  car- 
bon, while  carbon  will  dissolve  apparently  only  1  per  cent,  or  so 
of  iron. 

Just  as  some  substances  resist  all  our  efforts  to  make  them 
combine  chemically,  so  others  refuse  to  dissolve.  For  instance, 
several  salts  and  liquids  will  not  dissolve  in  water,  the  best  solvent 
known,  or  rather,  dissolve  to  such  a  slight  degree  that,  for  practical 
purposes,  it  may  be  neglected.  The  same  is  true  of  iron  and  mer- 
cury, melted  lead,  and  zinc,  etc. 

Essence  oj  Solubility.  —  Just  what  the  nature  of  the  state  of 
solution  is  cannot  be  told  at  present,  but  the  atoms,  or  molecules, 
of  the  dissolved  substance,  known  as  the  '  solute/  seem  to  be 
held  by  the  molecules  of  the  solvent.  One  striking  difference  ex- 
isting between  a  solution  and  a  mixture  is  that  the  solute  seems 
to  occupy  no  space.  If  we  mix  with  hot  water  one-quarter  of  its 


CHEMISTRY  AND  PHYSICS  481 

weight  of  table  salt,  the  level  of  the  water  will  rise  in  the  contain- 
ing vessel  an  amount  equivalent  to  the  bulk  of  the  salt,  but,  as 
soon  as  the  water  dissolves  the  salt,  it  will  fall  back  to  its  original 
volume.  In  short,  we  now  have  a  quarter  more  weight  of  ma- 
terial in  the  same  bulk,  so  that  the  specific  weight  of  the  mass 
increases  25  per  cent.  In  several  ways  which  we  have  not  space 
here  to  discuss  we  can  know  of  the  presence  of  a  greater  number 
of  molecules  than  ordinary  in  the  same  space  when  two  or  more 
substances  are  dissolved  in  each  other;  for  instance,  'osmotic 
pressure/  surface  tension.  Metals  dissolved  in  each  other  are 
heavier  than  the  same  bulk  of  any  of  the  metals  alone. 

Precipitation.  —  If  we  dissolve  27  per  cent,  of  table  salt  in  hot 
water  and  then  allow  the  water  to  cool,  some  of  the  salt  will  fall 
out  of  solution  again  and  crystallize.  This  action  is  called  t  pre- 
cipitation.' It  is  one  of  the  most  important  actions  in  chemis- 
try. We  may  cause  a  precipitation  by  another  means :  If  we  have 
as  much  of  any  salt  dissolved  in  water  as  it  will  take,  and  then 
add  to  the  solution  a  more  soluble  one,  the  water  will  dissolve  the 
new  salt  and  precipitate  the  old  one  in  corresponding  amount. 
The  same  applies  in  metallic  solutions:  If  we  have  5  per  cent,  of 
carbon  dissolved  in  iron  and  then  add  some  metallic  silicon,  the 
iron  will  precipitate  graphite  in  flakes  of  'kish/  and  dissolve  sili- 
con. The  commonest  method  of  precipitating  elements  in  wet 
chemistry  is  by  producing  chemical  change:  Suppose  we  have 
some  table  salt  (NaCl)  dissolved  in  water  and  add  just  enough 
silver  nitrate  (AgNOs)  to  react  with  it;  we  form  silver  chloride 
which  is  insoluble,  and  which  precipitates  almost  instantaneously : 

NaCl  +  AgNO,  -  AgCl  +  NaNO,. 

This  is  only  a  partial  precipitation,  because  sodium  nitrate  is  still 
left  in  solution,  but  is  often  of  great  service. 

Solubility  and  Temperature.  —  As  a  general  thing  the  higher 
the  temperature  the  greater  amount  of  solute  can  be  dissolved  in 
any  given  solvent.  This  rule  is  not  universal,  but  usually  applies 
in  practical  metallurgical  chemistry.  Five  per  cent.,  or  even 
more,  carbon  will  dissolve  in  iron  at  a  high  temperature,  but  some 
of  this  precipitates  as  the  metal  cools  near  its  solidification  tem- 
perature. 

Alloys.  —  Metallic  alloys  are  dependent  upon  solution  for  their 
formation.  Two  metals  which  will  not  dissolve  cannot  be  made 


482  THE  METALLURGY  OF   IRON  AND  STEEL 

to  form  alloys,  and,  in  practice,  all  alloys  are  made  by  dissolving 
melted  metals  in  each  other.  The  only  exception  is  certain  al- 
loys made  by  dissolving  solid  metals  in  each  other  under  great 
pressure. 

Nature  of  Slags.  —  Slags  are  molten  solutions,  and  as  a  gen- 
eral rule,  they  will  dissolve  all  the  oxidized  substances  with  which 
they  come  in  contact  in  the  furnace  (except  of  course  the  furnace 
lining  itself),  and  will  precipitate  all  the  reduced  substances.  For 
example,  metals  will  be  precipitated  as  fast  as  reduced  from  their 
combinations  in  the  ores:  phosphorus,  if  oxidized  by  being  com- 
bined with  some  base  as  a  phosphate,  will  be  dissolved,  but,  if 
silica  takes  the  base  away  from  it,  the  reduced  phosphorus  will  be 
precipitated  again. 

SOME  PRINCIPLES  OF  PHYSICS 

Dalton  and  Gay  Lussac  Law.  —  When  elements  or  compounds 
are  in  the  gaseous  form  they  all  expand  and  contract  at  the  same 
rate.  In  brief,  every  gas  expands  -^j-j  of  its  volume  for  every 
degree  Centigrade  that  the  temperature  is  increased,  and  ^T  for 
every  degree  Fahrenheit.  Air  or  steam  at  273°  C.  (491°  F.)  has 
twice  the  volume  of  the  same  weight  of  air  or  steam  at  0°  C. 
(32°  F.).  The  amount  of  increase  or  decrease  in  volume  can  be 
calculated  by  multiplying  its  volume  at  0°  C.  by  the  number  of 
degrees  increase  or  decrease  in  temperature  and  then  dividing 
the  product  so  obtained  by  273,  if  Centigrade  units  are  used,  or 
by  491.4  if  Fahrenheit. 

Boyle's  Law.  —  The  volume  of  gases  also  increases  or  de- 
creases in  proportion  to  lessening  or  increasing  the  pressure.  Or- 
dinarily gases  are  under  the  atmospheric  pressure,  which  is  15 
pounds  per  square  inch.  If  we  increase  the  pressure  upon  them 
to  30  pounds,  their  volume  becomes  one-half;  if  we  increase  it  to 
45  pounds,  it  becomes  one-third,  etc. 

Specific  Gravity.  —  The  specific  gravity  of  bodies  is  the  rela- 
tive weights  of  a  unit  volume.  For  example,  a  cubic  inch  of  iron 
weighs  nearly  8  times  as  much  as  a  cubic  inch  of  ice,  and  a  cubic 
inch  of  lead  or  platinum  weighs  more  still.  The  specific  gravity 
of  solids  and  liquids  are  usually  compared  with  water  as  a  standard, 
and  water  at  its  temperature  of  maximum  density  —  4°  C.  (39.2° 
F.)  —  is  given  an  arbitrary  value  of  1.  Gases  are  usually  com- 


CHEMISTRY  AND   PHYSICS  483 

pared  with  air  as  a  standard,  and  air  at  0°  C.  (32°  F.)  and 
under  a  pressure  of  760  millimeters  of  mercury  (  =  practically  15 
pounds  per  square  inch)  is  given  an  arbitrary  value  of  1.  (See 
page  27.) 

Avogadro's  Hypothesis.  —  Equal  volumes  of  all  gases  contain 
the  same  number  of  molecules.1  This  is  an  important  observa- 
tion and  leads  us  to  another:  that  the  specific  gravities  of  gases 
bear  the  same  relation  to  each  other  as  their  molecular  weights. 
In  other  words,  nitrogen  is  14  times  as  heavy  as  hydrogen,  and 
carbon  monoxide,  (CO)  14  times. 

Heat.  —  The  atoms  and  molecules  of  all  bodies  are  never  in 
a  state  of  Test,  even  though  the  body  itself  appears  to  be  quiet. 
It  is  this  constant  and  violent  motion  of  the  molecules  which 
we  know  under  the  name  of  heat.  To  raise  the  temperature  of  a 
substance  increases  the  motion  and  vice  versa.  In  the  case  of 
solids  the  vibration  of  each  molecule  is  of  course  confined  to  a 
very  small  space  indeed,  but  in  the  case  of  gases,  the  molecules 
travel  until  they  strike  against  some  other  body  with  force  enough 
to  resist  them,  as,  for  instance,  some  other  molecule,  or  the  walls 
of  the  vessel  in  which  they  are  contained,  when  they  move  with 
equal  velocity  in  another  direction.  It  is,  in  fact,  the  constant 
impact  of  molecules  upon  the  walls  of  the  containing  vessel  that 
causes  gases  to  exert  pressure.  This  explains  why  it  takes  twice 
as  much  pressure  to  confine  the  same  weight  of  a  gas  into  one- 
half  the  volume,  because  now  the  molecules  have  only  one-half 
as  far  to  travel  between  containing  walls  and  therefore  they  strike 
them  twice  as  often.  It  also  explains  why  gases  expand  when 
their  temperature  is  raised,  provided  the  pressure  under  which 
they  are  confined  remains  constant,  because  if  their  motion  is 
more  rapid  they  exert  greater  pressure  against  the  containing 
walls. 

Conservation  of  Energy.  —  The  law  of  conservation  of  energy 
tells  us  that  energy  can  be  neither  created  nor  destroyed.  We  can 
•convert  chemical  energy  into  heat,  or  heat  into  motion,  but  we 
cannot  get  energy  out  of  anything  into  which  we  do  not  put  an 
equivalent  amount  in  some  form  or  another.  We  may  waste 
energy,  such  as  energy  lost  in  heat  from  friction  which  is  useless 
to  us,  but  it  does  not  cease  to  exist. 

1  It  being  understood  of  course  that  the  conditions  of  pressure  and  tem- 
perature are  identical. 


484  THE  METALLURGY  OF   IRON  AND   STEEL 


PHYSICAL  PROPERTIES  OF  METALS 

Tensile  Strength.  —  The  tensile  strength  of  a  body  is  its  re- 
sistance to  being  pulled  asunder.  It  is  usually  measured  in 
pounds  per  square  inch;  that  is  to  say,  a  bar  of  wrought  iron  for 
example,  with  one  square  inch  cross-sectional  area1  will  support 
about  50,000  pounds  weight. 

Stress  and  Strain.  —  A  stress  is  a  force  put  upon  a  body,  and 
a  strain  is  the  deformation  of  the  body  produced  by  a  stress. 
For  instance,  if  a  bar  of  wrought  iron  one  square  inch  in  cross- 
sectional  area  and  2  inches  long  be  made  to  support  a  weight  of 
10,000  pounds,  it  will  stretch  about  0.0007  inch;  the  10,000  weight 
is  the  stress,  and  the  0.0007  inch  is  the  corresponding  strain. 

Elastic  Limit.  —  In  the  case  just  mentioned,  if  the  10,000 
weight  be  removed  the  strain  will  be  removed.  That  is,  the  bar 
will  return  to  its  original  length  of  2  inches.  Now  if  the  same  bar 
be  loaded  with  20,000  pounds  it  will  stretch  0.0014  inch,  and  again 
this  elongation  will  be  lost  when  the  weight  is  removed.  If,  how- 
ever, we  load  the  bar  with  30,000,  it  will  stretch  a  little  more  than 
0.0021  inch,  and  now  it  will  not  return  to  its  original  2-inch  length 
when  the  weight  is  removed,  but  will  be  permanently  elongated. 
It  has  taken  a  'permanent  set/  as  it  is  called.  The  '  elastic 
limit'  of  a  body  is  the  force  necessary  to  produce  the  first  per- 
manent set.  It  is  usually  measured  in  pounds  per  square  inch. 
Another  way  of  expressing  the  elastic  limit  is  to  say  it  is  the  force 
beyond  which  the  strain  is  not  proportional  to  the  stress. 

Modulus  of  Elasticity.  —  The  modulus  of  elasticity  tells  of  the 
resilience,  or  springiness,  of  a  body,  that  is  to  say,  how  much  it 
will  yield  under  any  stress  up  to  the  elastic  limit.  The  modulus 
of  elasticity  is  obtained  by  dividing  any  stress  up  to  the  elastic 
limit  by  the  strain  produced  per  inch  of  length.  For  example, 
the  wrought  iron  mentioned  in  the  last  paragraph  stretched 
0.0014  inch  in  a  length  of  2  inches,  =0.0007  per  inch  of  length, 
with  a  stress  of  20,000  pounds  per  square  inch;  its  modulus  of 
elasticity  will  then  be: 

20,000 


00007 

1  Say  a  round  bar  about  1^-inch  diameter,  or  a  square  bar  one  inch  on  a 
side. 


CHEMISTRY  AND  PHYSICS  485 

Percentage  Elongation.  —  After  a  bar  under  tensile  stress  has 
passed  its  elastic  limit  it  begins  to  be  permanently  elongated  in 
the  direction  of  the  pull.  A  soft  metal,  like  copper  or  mild  steel, 
will  stretch  out  somewhat  like  molasses  candy  before  finally  break- 
ing, and  may  be  almost  twice  as  long  as  it  was  originally.  The 
increase  in  length,  divided  by  the  original  length,  is  the  percentage 
elongation.  It  is  usually  measured  on  a  length  of  two  inches, 
or  of  eight  inches. 

Reduction  of  Area.  —  When  a  bar  is  elongated  it  of  course 
shrinks  in  cross-section;  finally,  just  before  the  bar  breaks,  it 
usually  ' necks  down'  directly  at  the  point  on  either  side  of  the 
fracture.  This  type  of  fracture  occurs  with  soft  metals.  The 
original  area,  minus  the  area  of  smallest  cross-section  after  frac- 
ture is  called  the  '  reduction  of  area/  and  this  divided  by  the 
original  area  is  the  'percentage  reduction  of  area.' 

Ductility.  —  The  percentage  elongation  and  the  percentage 
reduction  of  area  are  usually  taken  together  as  the  measure  of  the 
ductility  of  a  metal. 

Compressive  Strength.  —  The  compressive  strength  of  a  body 
is  its  resistance  to  crushing.  It  also  is  usually  measured  in  pounds 
per  square  inch.1  The  terms  ' stress  and  strain/  'elastic  limit/ 
and  '  modulus  of  elasticity '  all  have  the  same  meaning  when  re- 
ferred to  compressive  as  to  tensile  stresses. 

Transverse  Strength.  —  If  a  bar  one  inch  square  be  supported 
on  thin  edges  placed  twelve  inches  apart  its  resistance  to  a  force 
applied  half  way  between  the  supports  is  called  its  'transverse 
strength/  Here  again  we  have  the  same  terms,  'stress  and 
strain/  etc. 

Impact.  —  If  a  bar  be  supported  on  thin  edges  placed  a  certain 
distance  apart  and  then  a  falling  weight  be  allowed  to  strike  upon 
it  at  a  point  midway  between  the  supports,  its  resistance  to  this 
force  will  give  an  indication  of  its  strength  under  impact,  while 
the  amount  that  it  will  bend  before  breaking  will  indicate  its 
ductility  under  impact,  or  under  'shock/ 

Shearing  Strength.  —  The  resistance  of  a  body  to  being  cut 
in  two  by  a  pair  of  knife  edges,  is  called  its  shearing  strength.. 
Rivets  are  sometimes  tested  in  this  way,  because  they  are  sub- 
jected to  this  kind  of  stress  in  service. 

1  In  Great  Britain  they  often  use  long  tons  (2,240  Ibs.)  per  square  inch, 
instead  of  pounds,  both  for  tensile  and  compressive  stresses. 


486  THE  METALLURGY  OF   IRON  AND  STEEL 

Torsion.  —  The  resistance  of  a  bar  to  being  twisted  like  a  cork- 
screw is  called  its  torsional  strength.  The  number  of  twists  it 
will  endure  before  breaking  gives  an  indication  of  its  ductility 
under  this  stress. 

Repeated  Stress.  —  If  a  certain  kind  of  stress  be  applied  to  a 
body,  then  relieved,  applied  again,  and  so  on  alternately,  this 
class  of  test  is  called  '  repeated  stress/  A  metal  will  break  under 
many  applications  of  a  repeated  stress  much  less  in  amount  than 
that  required  to  fcreak  it  if  constantly  applied.  It  is  to  be  under- 
stood, however,  that  the  interval  between  the  applications  of  the 
stress  must  be  very  short  so  the  metal  will  have  no  opportunity 
to  rest  between  applications. 

Alternate  Stresses.  —  If  we  place  a  body  first  under  tension, 
then  under  compression,  and  so  on  alternately,  it  produces  what 
is  known  as  ' alternate  stresses.'  It  is  like  in  nature  to  bending 
a  wire  back  and  forth,  and  metals  will  break  under  alternate 
stress  even  less  than  their  elastic  limits  under  either  tension  or 
compression  alone. 

Toughness.  —  The  toughness  of  a  metal  is  its  resistance  to 
breaking  after  its  elastic  limit  is  passed.  It  is  the  direct  opposite 
of  brittleness. 

Brittleness.  —  The  brittleness  of  a  metal  is  the  ease  with  which 
it  breaks  after  its  elastic  limit  is  exceeded.  A  very  brittle  steel 
will  have  an  elastic  limit  exactly  equal  to  its  ultimate  tensile  or 
compressive  strength;  that  is  to  say,  it  will  take  no  permanent 
elongation  or  reduction  or  area;  its  ductility  will  be  zero.  Some 
metals  are  more  brittle  under  shock  than  under  constantly  applied 
stress,  and  vice  versa. 

Malleability.  —  Malleability  is  the  quality  of  being  deformed 
under  a  hammer.  Gold  is  the  most  malleable  of  metals  and 
can  be  hammered  into  sheets  of  extreme  thinness  without 
cracking. 

Resilience.  —  We  have  already  described  resilience  under  the 
head  of  modulus  of  elasticity.  A  very  resilient  metal,  that  is,  one 
with  a  small  modulus,  would  be  unsuitable  for  a  bridge  even 
though  strong,  because  its  vibration  under  a  moving  load  would 
be  so  great. 

Hardness.  —  The  hardness  of  a  metal  is  its  resistance  to  being 
scratched,  or  to  wearing  away  under  friction.  In  steel  metallurgy 
hardness  is  often  used  to  mean  brittleness,  but  this  is  no  longer 


CHEMISTRY  AND  PHYSICS  487 

advisable,  because  we  are  now  making  hard  steels  that  are  also 
tough. 

AUotropy.  —  Allotropy  is  the  capacity  that  certain  elements 
have  of  changing  their  properties  without  changing  their  com- 
position or  purity.  For  example,  we  may  have  pure  carbon  in 
the  form  of  diamond,  graphite  or  charcoal;  we  may  have  iron  in 
a  magnetic  or  non-magnetic  condition;  we  may  have  sulphur  in 
a  brittle  or  in  a  pasty  state,  etc.  What  the  nature  of  allotropy  is 
we  cannot  at  present  tell.  It  may  perhaps  have  to  do  with  the 
relations  of  the  different  atoms  in  the  molecules  of  the  element. 
When  elements  form  compounds  the  atoms  of  one  are  joined  to 
the  atoms  of  the  others,  and  even  when  elements  are  in  the  pure 
state  their  atoms  are  often  joined  together  to  form  molecules. 
Allotropy  may  be  a  difference  in  the  number  of  atoms  that  are  in 
each  molecule,  or  perhaps  in  the  form  in  which  they  are  joined 
together.  An  allotropic  change  -is  always  accompanied  by  a  loss 
or  gain  of  heat. 

Crystallization.  —  The  tendency  of  most  elements  and  com- 
pounds to  arrange  themselves  into  regular  forms  called  crystals 
is  really  a  powerful  force  of  Nature,  and  one  of  the  most  wonderful 
and  charming  studies  imaginable.  The  crystalline  forms  of  each 
particular  substance  are  usually  the  same,  or  very  similar,  but 
different  from  almost  all  other  substances.  Each  crystal  is  built 
up  of  smaller  crystals,  and  these  in  turn  of  still  smaller  ones. 
The  tendency  to  produce  a  regular  form  is  well  illustrated  in  the 
case  of  alum:  If  a  piece  of  an  alum  crystal  be  broken  off  and  the 
main  part  be  immersed  in  a  saturated  alum  solution,  the  crystal 
will  slowly  repair  itself  and  renew  the  lost  part  until  it  is  again 
perfect.  Moreover,  if  the  alum  solution  is  impure,  the  crystal  will 
take  to  itself  only  the  pure  salt,  and  leave  the  impurity. 


488 


THE   METALLURGY  OF   IRON  AND   STEEL 


TABLE  XXXIV.— COMPARISON  OF  DEGREES  CENTIGRADE  AND 

FAHRENHEIT 


Below  zero 

Above  zero 

Above  zero 

Equivalents 

C. 

-200°  = 

F. 
-328° 

C. 

+  525° 

F. 

=  +  977° 

C. 

+  1,250°  - 

F. 

2,282° 

C. 

1°  = 

F. 
1.8 

150  - 

238 

550 

-  1,022 

1,275  - 

2,327 

2  = 

3.6 

100  - 

148 

575 

-  1,067 

1,300  - 

2,372 

3  = 

5.4 

50  - 

58 

600 

-  1,112 

1,325  - 

2,417 

4  = 

7.2 

625 

-  1,157 

1,350  - 

2,462 

5  = 

9.0 

Above  zero 

650 

-  1,202 

1,375  = 

2,507 

6  = 

10.8 

C. 

F. 

675 
700 

-  1,247 

=  1,292 

1,400  = 
1,425  - 

2,552 
2,597 

7  = 
8  = 

12.6 
14.4 

25  - 

77 

725 

-  1,337 

1,450  = 

2,642 

9  = 

16.2 

50  - 

122 

750 

-  1,382 

1,475  - 

2,687 

10  = 

18.0 

75  - 

167 

775 

-  1,427 

1,500  - 

2,732 

11  = 

19.8 

100  - 

212 

800 

=  1,472 

1,525  - 

2,777 

12  = 

21.6 

125  - 

257 

825 

-  1,517 

1,550  - 

2,822 

13  = 

23.4 

150  - 

302 

850 

-  1,562 

1,575  - 

2,867 

14  = 

25.2 

175  = 

347 

875 

-  1,627 

1,600  = 

2,912 

15  = 

27.0 

200  - 

392 

900 

-  1,652 

1,625  - 

2,957 

16  = 

28.8 

225  - 

437 

925 

=  1,697 

1,650  = 

3,002 

17  = 

30.6 

250  - 

482 

950 

-  1,742 

1,675  - 

3,047 

18  = 

32.4 

275  = 

527 

1,000 

-  1,832 

1,700  = 

3,092 

19  = 

34.2 

300  = 

572 

1,025 

=  1,877 

1,725  = 

3,137 

20  = 

36.0 

325  - 

617 

1,050 

-  1,922 

1,750  = 

3,182 

21  = 

37.8 

350  - 

662 

1,075 

-  1,967 

1,775  = 

3,227 

22  = 

39.6 

375  - 

707 

1,100 

-  2,012 

1,800  = 

3,272 

23  = 

41.4 

400  - 

752 

1,125 

=  2,057 

1,825  - 

3,317 

24  = 

43.2 

425  - 

797 

1,150 

-  2,102 

1,850  = 

3,362 

25  = 

45.0 

450  - 

842 

1,175 

=  2,147 

1,875  - 

3,407 

475  - 

887 

1,200 

=  2,192 

1,900  = 

3,452 

500  = 

932 

1,225 

=  2,237 

2,000  = 

3,632 

INDEX  TO  AUTHORITIES  CITED 


ALLING,  GEORGE  W.,  395. 
AKERMAN,  RICHARD,  125,  183. 
ATHA,  HERBERT  B.,  245. 
AUSTEN.     See  ROBERTS-AUSTEN. 
ARNOLD,  J.  O.,  9,  332. 

BACON,  JOHN  LORD,  395. 
BAGSHAW,  WALTER,  457. 
BALE,  GEO.  R.',  291. 
BAKHUIS-ROOZEBOOM,   H.   W.,   312, 

315. 

BAUERMAN,  H.,  93. 
BAUSCH,  EDWARD,  457. 
BEHRENS,  H.,  457. 
BELL,  SIR  I.  LOWTHIAN,  67,  73. 
BENEDICKS,  CARL,  395. 
BLAIR,  A.  A.,  8,  144. 
BORCHERS  W.,  447. 
BRINELL,  J.  A.,  174. 
BROWNE,  D.  H.,  420. 
BURGESS,  C.  F.,  446,  447. 

CAMPBELL,  H.  H.,  8,  117,  152,  155, 

169,  326,  327. 

CAMPBELL,  WILLIAM,  377,  457. 
CARPENTER,  H.  C.  H.,  412,  421. 
CARTAUD,  C.,  332. 
CASPERSSON,  C.  A.,  183. 
CHARPY,  G.,  400. 
CHURCH,  A.  H.,  436. 
COLBY,  ALBERT  LADD,  400,  420. 
COLBY,  E.  A.,  442. 
CORT,  HENRY,  57. 
CUSHMAN,  ALLERTON  S.,  423,  436. 

DAELEN,  R.  M.,  197. 
DEER,  Louis,  457. 
DE  MOZAY,  421. 


DORMAN,  W.  H.,  94. 
DUMAS,  L.,  404,  420. 

FRITZ,  JOHN,  195. 

GAGES,  LEON,  73. 
GLEDHILL,  J.  M.,  421. 
GOERENS,  PAUL,  457. 
GUILLAUME,  C.  E.,  400,  420. 
GUILLET,  L.,  404,  408,  420,  421. 

HAANEL,  EUGENE,  447. 
HADFIELD,  R.  A.,  330,  405,  413,  420. 
HAMBUECHEN,  CARL,  447. 
HARBORD,  F.  W.,  72. 
HEYN,  E.,  457. 

HOERHAGER,    J.,    421. 

HOWE,  HENRY  M.,  8,  72,  86,  91,  125, 
177,  178,  182,  183,  184,  310, 
311,  335,  371,  375,  384,  385, 
394,  420,  427,  436. 

JOHNSON,  JR.,  J.  E.,  39,  174,  335. 
JUPTNER,  HANNS  FREIHERR  VON,  395. 

KEEP,  WILLIAM  J.,  291,  347. 
KERSHAW,  JOHN  B.  C.,  447. 
KJELLIN,  F.  A.,  442. 

LE  CHATELIER,  H.,  447,  455,  451. 
LEDEBUR,  A.,  72. 
LEWKOWITSCH,  436. 

LlLIENBERG,    N.,    184. 

MclLHiNEY,  PARKER  C.,  245. 
MCQUILLAN,  W.  S.,  279. 
MELLOR,  J.  W.,  395. 
METCALF,  WILLIAM,  379,  380. 


489 


490 


INDEX  TO  AUTHORITIES  CITED 


MOLDENKE,  RICHARD,  369. 
MONELL,  AMBROSE,  158. 
MUELLER,  FRIEDRICH  C.  G.,  125. 
MUSHET,  ROBERT,  408. 

NICOLARDOT,  P.,  421. 
NICOLSON,  J.  T.,  421. 
NOBLE,  H.,  73. 

OSMOND,  F.,  317,   330-2,   392,   453, 

457. 
OVERMAN,  FREDERICK,  94. 

PAVLOV,  M.  A.,  93. 
PERCY,  JOHN,  73. 
PHILLIPS,  J.  ARTHUR,  94. 
PHILLIPS,  W.  B.,  126. 
PROCHASKA,  ERNEST,  126. 

READ,  A.  A.,  332. 

RICHARDS,  J.  W.,  122,  125,  136. 

ROBERTS- AUSTEN,  SIR  WILLIAM,  312, 

314-15. 

ROE,  JAMES  P.,  77. 
ROOZEBOOM.     See   BAKHUIS-ROOZE- 

BOOM. 

Rossi,  A.  J.,  421. 
RYLAND'S  DIRECTORY,  8. 


SANITER,  E.  H.,  149. 

SAUVEUR,  ALBERT,  320,  332,  371,  394, 

395,  453,  455,  457. 
SCROLL,  GEO.  P.,  447. 
SCOTT,  W.  G.,  355. 
SMITH,  J.  KENT,  421. 
SPELLER,  F.  N.,  436. 
STANSFIELD,  ALFRED,  378,  379,  395. 
STEAD,   J.   E.,   182,    323,    332,   382, 

457. 
SWANK,  JAMES  M.,  8,  10. 


TALBOT,  BENJAMIN,  182,  184. 
TAYLOR,  FREDERICK  W.,  409. 
TRURAN,  W.,  94. 

TURNER,     THOMAS,     93,    291,    338, 
347. 

VATHAIRE,  A.  DE,  93. 

WATERHOUSE,  G.  B.,  332,  402,  403, 

404,  419. 

WEBSTER,  W.  R.,  326. 
WEDDING,  HERMANN,  72,  126. 
WEST,  THOMAS  D.,  291. 
WHITE,  MAUNSEL,  409. 
WOOD  WORTH,  JOSEPH  V.,  395. 


INDEX 


Acetylene,  469. 

Acid,  compared  with  basic  Bessemer, 
125. 

compared  with  basic  steel,  59. 

distinguished  from  basic  steel,  67. 

furnaces  for  steel  castings,  286- 

92. 
Acids,  definition  of,  471-72. 

effect  on  corrosion,  423. 
Acid  steel,  oxygen  in,  328. 

vs.  basic  furnaces  for  castings, 

287. 

Adulterants  in  linseed  oil,  432. 
After-blow  in  basic  Bessemer,  123. 
Agate,  476. 
Air,  amount  of  moisture  in,  38. 

and  moisture  producing  rust,  422. 

composition  of,  460. 
Air-furnace,    284-85,  286,  348,  352, 
358-62. 

compared  with  cupola,  361-62. 
Air-hardening  steel,  408. 

liquid,  462. 

necessary  to  burn  coke,  269. 
Alloys,  292,  481. 
Alloy  steels,  396-421. 

definition  of,  396. 
Allotropic     modifications     of     iron, 

317-19,  383,  384-86. 
Allotropy,  486. 

Alpha  iron,  318,  384-85,  393,  394. 
Alternate  stresses,  398,  415,  416,  418, 

485-86. 

Aluminum,  chemistry  of,  477-78. 
Aluminum  in  steel,  174. 
American  iron  and  steel  manufacture, 
scheme  of,  51-53. 

Lancashire  process,  71. 


Analysis,  461. 
Anhydrous  acids,  472. 
Animal  forms,  composition  of,  460. 
Annealing  boxes  for  malleable  cast- 
ings, 362. 

carbon,  320. 

malleable  castings,  52,  357,  358, 
364,  365,  366,  367,  370. 

ovens,  363. 

pots  for  malleable  castings,  362. 

steel,  224-25,  229,  370,  378,  382, 

383,  387-89,  412. 
Anthracite,  12. 
Anvils,  chilling  of,  352. 
Apatite,  478. 

Armor  plate,  227,  386,  398,  407. 
Arsenic,  effect  on  steel,  328. 
Atmospheric  pressure,  482. 
Atomic  weights,  466,  467. 
Atoms,  466,  471. 
Austenite,  305,  334,  338,  342,  389-95, 

407,  408,  413. 
Automobile  steels,  190-91,  408,  417, 

418,  419. 

Avagadro's  hypothesis,  482. 
Axles,  properties  of,  329. 

Baby  Bessemer  converters,  286-92. 
Badly  made  material  and  corrosion, 

427-29. 

Balling  in  puddling  process,  81. 
Bands,  65. 
Bar  iron,  70. 
Bars,  forging  of,  189. 

rolling  of,  196. 
Bases,  definition  of,  471-72. 
Basic  Bessemer  compared  with  acid, 

125. 


491 


492 


INDEX 


Basic  Bessemer  compared  with  acid 

steel,  59-60. 
distinguished    from    acid    steel, 

66-7. 

furnace  lining,  472. 
pig  iron,  42,  104,  146. 
process,  51,  122-25. 
slag,  471-72. 

steel  for  railroad  rails,  62-63. 
steel  in  U.  S.,  53. 
steel,  oxygen  in,  328. 
steel,  strength  of,  327. 
vs.  acid  furnaces  for  steel  cast- 
ings, 287. 

Bas-relief  polishing,  452. 
Bath  in  Bessemer  converter,  depth  of, 

102. 

Bearings,  properties  of,  329. 
Bed  of  cupola,  266,  269,  270,  274, 

280-84. 

Beehive  coke  oven,  12,  14,  16. 
Bell,  224. 

Bell-Krupp  process,  67-68. 
Bell  of  blast  furnace,  23. 
Bench,  226. 

molding,  243. 

Bertrand-Thiel  process,  159. 
Bessemer  blow,  96,  105. 
Bessemer  boil,  118. 

compared  with  open-hearth  steel, 

60-63,  287-88. 
converter,  98-102,  286-92. 
distinguished  from  open-hearth 

steel,  67. 

flames,  96,  105,  118,  119. 
fume,  118. 
gases,  116-17. 
ingots,  weight  of,  197. 
iron,  analyses  of,  95,  104. 
ores  defined,  61. 
pig  iron,  95. 
process,  53,  61,  95-126. 

recarburizing  in,  54,  60,  103-5, 

120. 

removal  of  impurities  in,  112- 
13,  114-15,  116,  122. 
j,   95,    100,    110,    113,    114, 
117-18. 


Bessemer  steel  in  U.  S.,  53. 

steel,  strength  of,  326. 

steel,  uses  of,  61-63,  224. 
Beta  iron,  318,  384-85,  394. 
Billets,  65,  196. 
Bi-prefix,  473. 
Bisilicate,  477. 
Biting  of  piece  by  rolls,  203. 
Bi-valent,  473. 

Black  heart  malleable  castings,  364. 
Black  iron,  435. 
Blast  furnace,  2,  11-50. 

chemistry  of,  30-91,  465. 

cinder.     See  Slags. 

dimensions  and  parts,  23,  24-28. 

fuels  and  fluxes,  11. 

limestone  used  in,  13. 

lining  of,  24,  25-26. 

ore  used  in,  amount  of,  13. 

slags,  37,  39-40. 

smelting  practice,  30. 

stoves.     See  Stoves. 

vs.  electric  furnace,  440-41. 
Blast  furnaces  in  United  States,  16. 
Blast,  in  Bessemer  process,  110. 

pressures  in  cupola,  264,  266, 
268,  269,  270,  271,  272,  273, 
280-3,  284. 

volumes   in   cupola.     See   Blast 

pressure. 
Blister  steel,  87. 
Blooming  rolls,  203,  220. 
Blooms,  65,  219. 
Blower  for  cupola,  268,  269. 
Blow-holes,  54,  59,  173,  174,  175,  185, 
287,  324,  341,  427,  428,  456. 
Blowing  engines  for  blast  furnace,  26, 

27. 

Blowpipe,  44,  168. 
Blue  powder,  434. 
'Body'  in  bar  iron,  70-71. 
Boil  in  puddling  process,  79. 
Boiler,  supports,  381. 

tubes,  224. 

Boilers  over  heating  furnaces,  231. 
Boiling  linseed  oil,  432. 
Boilings,  85. 
Boron  steels,  397. 


INDEX 


493 


Bosh  of  blast  furnace,  24,  25-26. 

Bottom  casting,  178. 

Bottoms  for  heating  furnaces,  233. 

Boyle's  law,  482. 

Brake  action  of  carbon,  385,  390. 

Breast  of,  blast  furnace,  25. 

cupola,  270. 
Breeze,  denned,  19. 
British  thermal  unit,  162,  171,  465. 
Brittleness,  defined,  486. 

of  Stead,  381-82. 

of  steel,  224,  327, 328-29, 386-87. 

See  also  Ductility. 
Bulldog,  75. 

Burdening  the  cupola,  273-77. 
Burglar-proof  safes,  195,  406. 
Burning  of,  molds  in  drying,  247. 

steel,  373-74,  378-80,  380-81. 
Busheling,  428. 
Butterfly  reversing  valve,  165. 
Butt-welded  tubes,  224. 
By-product  coke  oven.     See  Retort 
coke  oven. 

Calcining  siderite,  16. 

Calcium,  chemistry  of,  479. 

Calcium  chloride  used  in  open  hearth, 
149. 

Calcium  fluoride  used  in  open  hearth, 
149. 

Calculating   a   blast-furnace   charge, 
46-50. 

Calorie  defined,  465. 

Calorific  equation,  in  Bessemer  proc- 
ess, 120-22. 
of  basic  Bessemer,  124. 

Campbell  open-hearth  process,  159- 
60. 

Camera  for  micro-photography,  454- 
55. 

Cannon,  192,  193,  227. 

Carbide  of  iron.     See  Cementite. 

Carbon,  5. 

Carbon.     See  also  Graphite  and  Com- 
bined carbon, 
as  a  reducing  agent,  474. 
chemical  affinity  for  iron,  6. 
chemistry  of,  475-76. 


Carbon,  control  of  in  pig  iron,  342. 
in  air  furnace,  284. 
in  iron  and  steel,  3,  51,  54,  63,  92, 
159,    180-83,    325-26,   327, 
329,  330,  336,  337-41,  370- 
74,  383,  385,  398,  405,  407, 
414,  446,  481,  423,  480. 
in  the  blast  furnace,  33. 
Carbonates,  475,  476,  479. 
Carbonic  oxide,  463. 
Carbonists,  385. 
Carbon  monoxide  as  a  reducing  agent, 

474. 

Carbon,  oxides  of,  475-76. 
of  cementation,  ,320. 
of  the  normal  carbide,  320. 
steel,  396. 

theory  of  hardness,  383,  384. 
Carburization  of  wrought  iron,  the, 

85-94. 

Car-casting  process,  107-8. 
Car  wheels,  328-29,  337,  343-44,  352. 
Case-hardening,  201,  408. 
Casting  bed  of  blast  furnace,  42. 
Casting  house  of  blast  furnace,  43. 
Castmgs,  65,  261,  380-81. 

compared     with     drop-forgingi,, 

189. 
Casting  temperature  o\  steel  ingots, 

60-61,  176,  183. 
Casting  with  large  end  up,  178. 
Cast  iron.     See  also  Blast  furnace, 

Pig  iron. 

checking  of,  355,  349-50. 
chilling  of,  253,  352-55,  336,  370. 
constitution  of,  333-55. 
corrosion  of,  425-26,  428-29. 
definition  of,  6,  11. 
description  of,  3. 
density  of,  347. 
fluidity  of,  341,  361. 
gray,  as  impure  steel,  335. 
color  due  to,  334. 
cooling  curve  of,  339. 
definition  of,  7. 
density  of,  347. 
photomicrograph  of,  353. 
properties  of,  334-55. 


494 


INDEX 


Cast  iron  pipe,  278,  425-26,  433. 
properties  of,  333-55. 
rate  of  cooling  of,  326. 
rolls,  201. 

shrinkage  of,  260,  261-62,  337- 
40,  341,  345-46,  347,   350, 
365,  367,  482. 
skin  of,  426,  429. 
softness  of,  350-52. 
solidification  of,  338,  339,  341. 
spongy  spots  in,  340,  347,  348. 
steel  scrap  in,  348,  351,  366-67. 
strength  of,  341, 347, 350-52, 364. 
vanadium  in,  419. 
vs.  steel,  333. 

workability  of,  340,  350-52. 
white,  definition  of,  7. 
properties  of,   etc.,  220,  253, 
334,  336,  339,  347,  352-55, 
357. 

Cast  steel,  66,  87,  368,  381. 
Cement  manufacture  from  slag,  39. 

carbon,  320. 

Cementation  of  iron,  34,  85,  86,  87. 
Cementite,   86,   304,   309,   311,  313, 
314,  316,  320-21,  323,  325- 
28,  334,  342,  345,  373,  389, 
390,  392,  394,  404,  425. 
Centigrade,  465,  487. 

converted  to  Fahrenheit  degrees, 

487. 

Chain  rods,  65. 
Chaplets,  250. 
Characteristics  of  acid  open  hearth, 

55-56. 

of  basic  open-hearth  process,  57. 
of  Bessemer  process,  54. 
Charcoal,  12,  90,  441,  474,  475. 
fineries,  69. 
hearth,  Walloon,  70. 
iron,  12,  353. 

Checking,  173,  241,  246,  248,  261. 
Chemical  affinity,  459,  461,  464. 
changes,  458-82. 
compounds,  293,  303,  471,  474- 

81. 

energy,  464,  471. 
equations,  466-69. 


Chemical  reactions,  474-79. 

stability,  473. 

symbols,  467,  471. 

Chemistry  and  physics  introductory 
to  metallurgy,  458-87. 

of  Bessemer  process,  53. 

of  crucible  process,  93. 

of  puddling,  57. 
Chicago  as  an  iron  center,  12. 
Chilling  castings,  201,  262,  336,  350. 
Chill  molds,  253,  255. 
Chisels,  388,  430. 
Chocks,  205. 
Chrome  steel,  195,   396,   397,   407-8, 

409,  413,  415,  416,  417. 
Chromic  acid  and  corrosion,  424. 
Chromium,  effect  on  crystallization, 

374. 
Cinder,  blast  furnace,  13. 

in  puddling  process,  85. 

notch  of  blast  furnace,  25. 
Clay,  477. 

iron  stone,  15. 

Cleaning  blast  furnace  gas,  30. 
Clearing  stage  in  puddling,  78,  82. 
Cleveland,  England  district,  iron  ores, 

15. 

Closed  pass,  200. 
Coarse-grained  steel,  370. 
Coating  of  wrought  iron,  428. 
Cobalt  steels,  397. 
Coefficient  of  friction,  400. 
Cogging  mill,  198,  202. 
Coke,    12,   13,  17,   91,  440-41,   474, 

475. 

Colby  induction  furnace,  441-44. 
Cold  short,  348. 
Cold  shut,  178. 

work  compared  with  hot  work, 

229,  328. 

Collars  on  rolls,  197. 
Collaring,  206,  215. 
Colors,  temper,  387. 
Combined  carbon  in  iron,  334-51. 
Combustion,  463,  466. 
Coming  to  nature   in   puddling,   58, 

179. 
Comparative  cupola  practice,  279-84. 


INDEX 


495 


Comparison  of  purification  processes, 

59-65. 
Compressive  strength  of  steel,  324, 

485. 
Compromise   theory  of  hardness   of 

steel,  385. 

Concentrator,  magnetic,  278. 
Connellsville  coke,  13. 
Conservation  of  energy,  483. 
Constitution  of  steel,  the,  316-32. 
Constituents  of  hardened  and  tem- 
pered steels,  389-95. 
Continuous    heating    furnaces,    230, 

23i;  232. 

Contraction.     See  Shrinkage. 
Converting  pots,  86. 
Cooling  curve  of  pure  iron,  319. 
curves,  300,  339. 
of  blast  furnace,  24. 
rate  of.     See  Rate  of  cooling, 
steel,  380-81. 
strains,  261-62. 
table,  221. 
Cope,  238,  250. 
Copper,  cooling  curve  of,  339. 

effect  on  steel,  327-28. 
Cores,  238-39,  241,  249,  250,  246-53, 

259. 
Corrosion  of  iron  and  steel,  the,  64, 

401,  422-36. 
Country  heat,  87. 
Critical  range  of  steel,  310,  314,  330, 

370-75,    382-95,    386,    388, 

401,  402,  407,  413. 
Critical    temperature     in     Bessemer 

process,  110-11. 
Crucible  furnaces,  87-91,  286. 

process,  85-87,  90,  92,  397,  444. 
steel,  52,  53,  63,  66-67,  74-94, 

195,  326. 

Crystalline  forces,  293. 
Crystallization  of  iron  and  steel,  179, 

186,  224,  261,  293,  318,  323, 

325,    370-82,  392-93,  398- 

99,  481,  487. 

Crystals  of  steel,  growth  of,  376. 
Cuban  ore  used  in  U.  S.,  17. 
Cupola,  262-85,  348,  354,  358. 


Cupola   charge,    270,    271,    273-79, 

280-82. 
chemistry  of,  271-73,  274,   278, 

284,  365. 
coal  in,  279. 
coke  in  iron,  264. 
compared     with     air     furnace, 

361-62. 

crucible  zone  of,  264,  266. 
dimensions,  267,  280-82. 
limestone  in,  271. 
lining  of,  267,  268,  270,  271,  272, 

280-82. 
melting  in,  270-71,  278-79,  280- 

82,  284. 

run,  or  campaign,  278-79. 
time  of  melting  in,  266,  267,  270, 

278-79,  280-83,  284. 
used  for  Bessemer  process,  97. 
Cutting  of  molds,  246. 

Dalton  and  Gay  Lussac  law,  482. 
Dannemora  iron  ore,  70. 
Dead  rollers,  210. 
Decomposition,  461,  464. 

of  iron  solid  solution,  309, 310-15. 
Defects  in  ingots,  173-84. 
Definitions  of  iron  and  steel,  66. 
Delays  in  rolling  mills,  206,  215. 
Dellwik-Fleischer  gas,  171-72. 
Density,  482. 

of  cast  iron,  347,  349. 
Dental    instruments,    tempering   of, 

387. 

Deoxidising  steel,  477. 
Depth  of  chill  in  cast  iron,  354-55. 

See  also  Chilling. 
Descent  of  charge  in  blast  furnace, 

30. 

Developing   structure   for   metallog- 
raphy, 452. 
Diamond,  384,  475. 

form  of  carbon  in  steel,  318. 

pass,  200. 
Dies.     See  Wire. 
Direct  castings,  262. 
Dirt  and  corrosion,  428,  429. 
Dirty  cast  iron  and  sulphur,  341. 


496 


INDEX 


Distinguishing  between  different  prod- 
ucts, 66. 
Dolomite,  479. 
Double  heat  treatment,  414. 
shear  heat,  87. 
steel,  87. 

Doubling  in  tin-plate  rolling,  61. 
Down-comer  of  blast  furnace,  30. 
Draft,  215. 

in  rolling,  220. 

in  wire  drawing,  224-25,  226. 
Drag,  238. 
Drawing,  of  wire.    See  Wire. 

temper,  388. 

Dried  air  in  blast  furnace,  38. 
Driers  in  paint  oils,  432. 
Drop-forging,  189,  190-91,  368. 
Drop  of  cupola,  271,  279. 
Dry  chemistry,  475. 
Drying  oil,  431. 
Drying  ovens,  243,  249. 
Dry-sand  molds,  237,  243,  245-48. 
Ductility,  defined,  485. 

of  metals,  measure  of,  187. 

of  steel,  67,  324,  325,  326,  328, 

329,  371,  387,  486. 
as  affected  by  forging  tempera- 
tures, 189. 
as     affected     by    mechanical 

work,  185. 

as  affected  by  oxygen,  328. 
as  affected  by  welding,  378. 
Dull  iron,  264. 

Duplex  process,  157,  158-59. 
Duplicating  patterns,  260. 
Dust-catcher  of  blast  furnace,  30. 

Earth's  crust,  composition  of,  460. 

Eccentric  converter,  99,  100. 

Effect  of  work  on  steel,  rationale  of, 

187. 
Elastic  limit,  defined,  484. 

of    carbon    and     nickel    steels, 

399. 
of  steel,  compared  with  ultimate 

strength,  187. 
of  welded  pieces,  378. 
when  exceeded,  186. 


Elastic  limit,  ratio,  399. 

Electric,  conductivity  of  steel,  329-30, 

414. 

furnaces,  419. 
motors  in  rolling  mills,  206,  208, 

209,  212,  213-15. 
resistance,  decrease  on  cooling, 

385,  394. 
resistance,  loss  of  in  tempering, 

387,  394. 

Electro-chemistry,  470. 
Electrolysis,  defined,  470. 

and  corrosion,  423,  423-29. 
Electrolytic,  iron,  321. 

refining,  437,  446-47. 
Electrometallurgy  of  iron  and  steel, 

the,  437-47. 
Electroplating,  433-35. 
Electro-thermic  processes,  437,  447. 
Elements,  460,  461,  466,  467,  471. 
Elongation,  of  steel  under  strain,  186. 

percentage  of,  defined,  484. 
Enameling,  435. 

Engraving  tools,  tempering  of,  387. 
Etching     for     metallography,     448, 

452-53. 
Ethylene,  469. 

Eutectic  alloy.     See  Eutectics. 
Eutectic  not  a  chemical  compound, 

303. 
Eutectics,  299-305,  306-8,  311,  312- 

15,  338. 

Eutectoid,  311-15,  325. 
Expansibility  of  steels,  400. 
Expense  in  puddling  process,  83. 
Explosion    doors    of    blast    furnace, 

44. 
Explosions  in  blast  furnace,  44. 

Fahrenheit,  465,  487. 

converted  to  centigrade  degrees, 

487. 

Fatigue  of  steel,  398,  415. 
Feeders  on  castings,  177.     See  also 

Risers. 

Feldspar,  477. 
Ferric  compounds,  473. 

oxide  as  a  pigment,  432. 


INDEX 


497 


Ferrite,  310,  311,  313,  316-19,  321, 
323,  325,  329,  330-32,  334, 
357,  371-73,  389,  392. 
Ferroalloys,  437. 
Ferro-chrome,  437. 
Ferromanganese,  90,  104,  397,  405. 
Ferro-molybdenum,  437. 
Ferro-nickel,  397. 
Ferrophosphoms  added  to  basic  steel, 

61. 

Ferrosilicon,  104,  274,  351. 
Ferro-tungsten,  437. 
Ferrous  compounds,  473. 

hydroxide  in  corrosion,  423-24. 
Ferrum,  467. 
Fertilizers,  478. 

Fettling  of  puddling  furnaces,  74-75. 
Fibers  in  wrought  iron,  58. 
Field  vs.  shop  painting,  430. 
Fillets  in  patterns,  261. 
Fin,  200,  215. 
Finery  fire,  68. 
Fingers  on  manipulator,  204. 
Finishing    temperatures   for   rolling, 
194-95,229.   .  See  also  Tem- 
peratures. 

Fireclay  crucibles,  90. 
Fir-tree  crystals,  182,  183. 
Five-ply  plate,  195. 
Flanging,  229. 
Flask,  238. 
Flint,  476. 

Floor-rammers,  242-43. 
Fluorspar,  149,  271. 
Flushing  a  blast  furnace,  39,  40. 
Fluxes,  blast  furnace,  11,  13. 
Fly-wheels  on  rolling  engines,  210, 

212. 

Forge  iron,  74,  104. 
Forging.     See  also  Hammering,  and 
Pressing. 

compared  with  rolling,  229. 

drop-,  189. 

finishing  temperatures  for,  189. 

of  metals,  the,  187-93,  227-29. 
Foundry    irons,    analyses    of,    104, 
274. 

ladles,  265. 


Foundry  practice,  236-92. 

Fracture  of  steel,  370,  454.     See  also 

Crystallization. 
Freezing,  44-45,  179,  186,  293.     See 

also  Solidification. 
of  alloys  of  lead  and  tin,  295-304. 
of  iron  and  steel,  304-15. 
Freezing-point  curves,  294,  300-15. 
Fuels,  11,  83,   93,    160-72,    229-35, 

264,  286,  363-64. 
Furnace  linings,  477,  479,  481. 

Galvanizing,  422,  429,  433-34. 
Gamma  iron,  318,  384,  385,  389,  393, 

394. 

Ganister  for  converter  lining,  99. 
Gas  engines  utilizing  blast  furnace 

gas,  31. 

Gaseous  fuels,  475. 
Gases  from  baby  Bessemer,  290-91. 

from  cupola,  272-73. 
Gas  mains,  165. 

producer  grate  area,  162. 

producers,  129,  160-64,  171. 
Gayley's  air-drying  process,  38-39. 
Gay  Lussac  and  Dalton  law,  482. 
Gate,  240,  241. 
Gated  patterns,  255. 
Gears,    properties   of,   32S-29,    408, 

419. 

Gold,  486. 

Goldschmidt  Thermit  process,  405. 
Gold-silver  alloys,  293-95, 304,  480. 
Grading  cast  steel  by  eye,  92-93. 
Grain  of  steel.     See  also  Crystalliza- 
tion of  steel. 
Graphite,  475. 

and  corrosion,  425. 

and    expansions.     See  Graphite 
and  Shrinkage. 

and  manganese,  344. 

and  phosphorus,  344-45. 

and  porosity,  340. 

and  shrinkage,  337-40,  345,  347. 

and  silicon,  343. 

and  strength,  337,  340-41,  351, 
356. 

and  sulphur,  343. 


498 


INDEX 


Graphite  and  workability,  340. 

as  a  pigment,  432. 

distinction  under  the  microscope, 
452. 

crucibles,  90. 

for  washes,  243-45. 

in  cast  iron,  333-55,  481. 

in  steel,  333. 

precipitation  in  malleable  cast- 
ings, 357. 

properties  and  structure  of,  334. 
Grease  producing  corrosion,  429. 
Green-sand  molds,  237,  243,  245-48. 
Grooved  rolls,  198,  200,  201,  202,  204, 

207, 208. 
Guards,  206. 
Guides,  205,  207. 

Hacksaws,  tempering  of,  387. 
•Hammering.     See  also  Forging, 
compared  with  rolling,  193. 
control  of  temperatures  in,  189. 
effect  of,  188-89,  375-78. 
Hammer  refining,  378.     See  also  Re- 
storing. 

Hand  rammers,  242-43. 
Hanging  guards,  206. 

of  blast  furnace  charge,  44. 
Hardened  steel,  constituents  of,  389— 

95. 

uses  of,  386. 

Hardening  of  steel,  382-95. 
and  magnetism,  330. 
theories  of,  383-86. 
Hardenite,  392. 
Hardness.     See  also  Workability  (for 

cast  iron), 
defined,  486. 
of  cast  iron,  347. 
of  cast  iron  and  manganese,  341. 
of  nickel  steel,  400. 
of  steel,  325,  328-29. 

as  affected  by  cold  work,  224. 
as  affected  by  forging  temper- 
atures, 189. 

due  to  carbon  alone,  411. 
loss  of  in  tempering,  387. 
loss  of  on  annealing,  385,  394. 


Hardness    produced    by  quenching, 

195,  382-95. 

Harmet's  liquid  compression,  179. 
Head,  or  header.     See  Riser. 
Hearth  of  blast  furnace,  24. 

of  cupola.     See  Crucible  zone. 
Heat,  definition  of,  483. 

effects  of  chemical  reactions,  11. 

energy,  471. 

from  chemical  change,  459,  470. 
See  Thermo-chemistry. 

in  rolling,  219. 

in  Bessemer  process,  60. 

tinting,  452-53. 

to  start  chemical  change,  459, 
460,  461,  462,  463,  464-66, 
470-71,  475-76,  479. 

treatment  of  cast  iron,  370. 

treatment  of  steel,  the,  370-95. 

units,  465. 

Heating  for  rolling,  etc.,  193, 217, 219, 
220,  380. 

furnaces,  229-35. 

of  steel,  improper,  370-82. 
Helve  hammers,  187. 
Hematite,  14. 
H6roult  process,  438-41,  444-46. 

steel  process,  444-46. 
Heyl  and  Patterson  pig-casting  ma- 
chine, 41. 

High-carbon  steel,  rolling  of,  235. 
High-speed  steels,  408-13,  415. 
Hollow  wire.     See  Tubes. 
Hoops,  65. 

Hopper  of  blast  furnace,  23,  24. 
Horns  on  manipulator,  204. 
Horse-shoe  bars,  65. 
Hot-blast  for  blast  furnace,  24,  27. 
Hot  iron,  361. 
Hot  spots  in  cast  iron,  349. 
Hot  work  compared  with  cold  work, 

229. 

Housing  cap,  205,  207. 
Housings,  204-12. 

Hughes    mechanically    poked    gas- 
producer,  164. 

Hydraulic  presses  compared  with  ham- 
mers, 188,  193,  227-28,  229. 


INDEX 


499 


Hydro-carbons,  433,  469-71. 
Hydrochloric  acid  for  etching,  454. 
Hydrogen  and  corrosion,  423,  430. 
Hydrogen,  chemistry  of,  469-71. 

in  Bessemer  steel,  60. 

in  crucible  steel,  63. 

in  iron,  446,  476. 

in  steel,  173,  324,  381. 

Illuminating  gas,  469. 
Impact,  485. 

Impurities  in  cast  iron,  effect  of,  342. 
Incomplete  combustion,  463. 
Indestructibility  of  matter,  468. 
Induction  furnaces,  440,  441,  442-44. 
Ingotism,  173,  179-80,  197,  235,  381. 
Ingot  molds,  92,  107-8,  111. 
Ingots  of  large  size,  form  of,  192. 

heating  of,  192. 

solidification  of,  177. 

taper  of,  220. 

texture  of  center  of,  193,  349, 

454. 

Inorganic  chemistry,  474-75. 
Iodine  etching,  453. 
Internal  stress  theory  of  hardness, 

386. 

Invar,  400-1. 
Invention  of  puddling,  57. 
Ionic  hydrogen  and  corrosion,  423. 
Tron.     See  also    Cast  iron,  Pig  iron, 
Wrought  iron,  Malleable  cast 
iron,  Malleable  iron. 

abundance  of,  4. 

and  carbon,  6. 

castings,  333. 

chemistry  of,  476. 

cupola.     See  Cupola. 

density  of,  347. 

foundries,  use  of  Bessemer  in, 
288. 

hardness  of,  383. 

melting  point  of,  446. 

occurrence  of  in  earth,  4,  461. 

ore  as  pigments,  432. 

ores  described,  14. 

oxide.     See  also  Oxygen. 

specific  gravity  of,  334. 


Iron,  strength  of,  324. 
Irregularities  in  blast-furnace  work- 
ing, 42-45. 

Irreversible  transformations,  402, 404. 
Isomorphous  mixtures,  293,  318. 

Jail  bars,  195. 

Jasper,  476. 

Jobbing  foundries,  use  of  scrap  in,  278. 

Keller  process,  438-41. 
Killing  in  crucible  process,  91. 
Kish,  481. 

Kjellin  electric  furnace,  440. 
Knobbled  charcoal  iron,  68. 

iron,  70. 

Knobbling  fire,  68,  69,  70. 
Krupp  purification  process,  67-68. 

Ladles,  foundry,  265. 

Lag  in  heating  and  cooling,  312. 

Lake  Superior  iron  ores,  14,  16,  17. 

Lancashire  process,  70-72. 

Lap-welded  tubing,  making  of,  221- 
22. 

Latent  heat  of  fusion,  301. 

Lathe  tools,  tempering  of,  387. 

Law  of  smelting,  466. 

Layers  of  iron  and  coke  in  cupola,  266, 
267,  269,  274,  280-84. 

Le  Chatelier  microscope,  455. 

Lead,  462-63.     See  also  Paints, 
and  zinc,  480. 
coatings,  434. 
in  terne  plate,  435. 

Lead-tin  alloys,  295-304. 

Lifters,  242. 

Lifting  screw,  238. 

Lilienberg's  liquid  compression,  179. 

Lime,  473,  479.  See  also  Blast  fur- 
nace, Open  hearth,  Cupola. 

Limestone,  33,  475,  479.  See  also 
Blast  furnace,  Open  hearth, 
Cupola. 

Limonite,  15. 

Linseed  oil,  431-32. 

Liquid  air,  462. 

Liquid  cast  iron,  density  of,  347. 


500 


INDEX 


Liquid  compression  of  ingots,  179. 

Live  rollers,  207. 

Loading  a  blast  furnace,  22. 

an  ore  boat,  19. 
Loam  molding,  236-38,  255. 
Long-tuyere  converters,  289-90. 
Loose  texture  in  center  of  castings, 

349.    See  also  Ingots. 
Loss,  in  air  furnace,  285. 

in  baby  Bessemer  converters,  288, 
289,  290. 

in  Bessemer  process,  118-19. 

in  crucible  process,  93. 

in  cupola,  264,  278. 

in  puddling  process,  83-84. 

in  rolling  plates,  219. 
Lorraine  iron  ore,  15. 
Lothringen  iron  ore,  15. 
Low-carbon    steel    in    open  hearth, 
making  of,  149. 

steels,  ferrite  in,  317. 
Luminosity  of  flames,  164,  165. 
Luxemburg  iron  ore,  15. 

Magnesia,  46-47,  477,  479. 
Magnesite,  479. 
Magnesium,  chemistry  of,  479. 
Magnetism  of  iron  and  steel,  4, 330-32, 

385,  389,  394. 
Magnetite,  15. 
Magnet  steels,  413,  414. 
Magroscopic  metallography,  448,  454- 

57. 
Malleable,  Bessemer  iron,  365. 

cast  iron,  53,  284-86,  351,  356- 

69. 

annealing  of,  370. 
as  steel  castings,  66,  368-69. 
definition  of,  7. 
description  of,  4. 
melting  of,  in  cupola,  264. 
properties  of,  356,  357-58. 
strength  of,  351,  364. 
uses  of,  356. 
coke  iron,  365. 
iron,  369. 
Malleability,  486. 
Mandril,  222,  226. 


Manganese,  chemistry  of,  478. 
as  a  reducing  agent,  474. 
and  sulphur,  341,  343-44. 
in  acid  open  hearth,  152,  155. 
in  basic  process,  146,  396. 
in  Bessemer  process,  95, 102,  113. 

396. 

in  blast  furnace,  38. 
in  cast  iron,  329,  335,  341,  342, 
343-44,  346,  348,  349,  350, 
351,  352,  354,  366,  374.    See 
also  in  steel, 
in  cupola,  274. 

in  steel,  54,  64,  66,  67,  174,  182, 
322-23,  327,  328,  330,  396, 
405-7,  427. 
in  wrought  iron,  66. 
oxides,  473. 

salts  as  paint  driers,  432. 
steel,  329,  396,  397,  405-7,  408. 
sulphide,  98,  316,  321,  322,  343, 

349. 

Manganiferous  cementite,  320—22. 
Manipulators,  210,  204. 
Manufacture.     See  Pig  iron,  Wrought 

iron,  Steel,  etc. 
Marble,  475. 
Martensite,  389-95. 
Match  for  molding,  251. 
Maximum  affinity,  464. 
Mechanical  gas  producers,  112,  161. 
mixtures,  459,  479. 
puddling  furnace,  68,  76. 
treatment,  effect  on  crystalliza- 
tion, 375-78. 
treatment    of    steel,    the,    185- 

235. 
work,  its  effect  on  strength,  etc., 

185. 

Melting,  fineries,  69. 
heat,  87. 
holes,  87-88. 

iron.     See  also  Cupola,  Air  fur- 
nace,   Open-hearth  furnace 
for  iron, 
-point  of  cast  iron.     See  Fluidity 

of  cast  iron, 
steel  for  castings,  286-92. 


INDEX 


501 


Melting    zone  of    cupola,  264,  266, 

267,  268,  272,  279-84. 
Merchant  bar,  58,  65. 
Mercury  and  iron,  459,  480. 
Mesabi  iron  ore,  19,  44. 
Metal-cutting  tools,  tempering  of,  387. 
Metallic  and  non-metallic  elements, 

471. 

lustre,  471. 
Metallography  of  iron  and  steel,  the, 

448-57. 

Metallurgy,  definition  of,  461. 
Metcalf  test,  379-80. 
Methane,  469. 
Mica  schist  for  converter  lining,  99- 

100. 
Micro-constituents  of  steel,  the,  316- 

32. 
Micro-photographic   apparatus,  454- 

55. 
Microscope,   316-24,   353,   370,   380, 

390-95,  392,  404,  448-57. 
Mill  iron,  74. 

Mill  scale.     See  also  Scale. 
Mineral  oil.     See  Petroleum  and  Oil 

for  Fuel. 

Minette  iron  ore,  15. 
Mining  ore  at  Lake  Superior,  19. 
Miscellaneous  purification  processes, 

67-72. 

Mixed  crystals,  293. 
Mixer,  95-97,  102,  262. 
Mixtures,  293.     See  Mechanical  mix- 
tures. 

Modulus  of  elasticity,  399-400,  484. 
Moisture   producing   corrosion,    422, 

429,  430. 
Mold  cars  for  car-casting  process,  107- 

8. 

Molders'  tools,  242. 
Molding  machines,  237,  251-60. 

sand,  243. 

Molds,  making  of,  237-62. 
Molecules,  468,  482. 
Molybdenum  steel,  396,  409-13. 
Mond  gas,  172. 
Monell  process,  157,  158. 
Monkey  of  blast  furnace,  25. 


Mono-,  prefix,  473. 

Monosilicate,  476. 

Morgan,  water  sealed  gas  producer, 

163. 
Mother  metals,  302. 

liquors,  302. 
Mottled,  cast  iron,  7,  347. 

pig  iron,  definition  of,  7. 
Muck  bar,  58. 
Multiple,  molds,  259. 

proportions  of  atomic  weights, 

467. 

Multiple-ply  plate,  195. 
Mushet  steel,  408-11. 
Mushroom  reversing  valves,  166,  167. 

Nailing  molds,  240,  247. 
Nail  plate,  65. 
Natural  gas,  166-68,  469. 
Necking  of  steel,  407,  484. 
Needles,  tempering  of,  387. 
Net  heat  of  chemical  reactions,  465. 
Neutral  furnace  linings,  477. 
Nickel,  effect  on  crystallization,  374. 
effect  on  electric  conductivity, 

330. 
Nickel-plating,  229,  435. 

steel,  202,  288,  396,  397,  398- 

404,  407,  408,  415,  416-19. 
uses  of,  398,  400-1. 
Nitric  acid  etching  for  metallography, 

452-53. 

Nitrogen  in  the  blast  furnace,  32. 
in  steel,  60,  63,  173,  324,  381, 

415,  419. 
Non-magnetic  iron  or  steel,  318,  404, 

407,  408,  409. 
Northampton  cast  iron,  cooling  curve 

of,  339. 
Norway  iron,  317. 

iron  for  magnets,  330. 
Nozzles  of  steel  ladles,  106. 
Number  of  Bessemer  converters  in 

America,  51,  52. 
blast  furnaces  in  America,  51, 

52. 

open-hearth  furnaces  in  Amer- 
ica, 51,  58. 


502 


INDEX 


Number     of    puddling    furnaces    in 
America,  51,  53. 

Oil  for  fuel,  169-70. 

Oolitic  hematite,  15. 

Opal,  476. 

Open   grain   in   cast  iron,  180,  340, 

347-48. 

Open-hearth   casting  pit,    131,    142, 
143,  151. 

bath,  138. 

boil,  148. 

bottom,  138-39. 

Campbell  type,  142-44,  159-60. 

charging,  155-56. 

charging  boxes,   128,   130,   131, 
140. 

charging  machines,  127, 128, 129, 
130-31. 

chimney,  136-37. 

construction,  138-39. 

cycles,  127. 

dirt  pockets,  132,  134,  135. 

draught,  136-37. 

for  melting  iron,  285-86,  362. 

fuels,  144,  155,  160-72. 

fuels,    amount   used,    144,    155, 
167,  169. 

furnace,  56,  442,  444. 

hearth,  138-39. 

house,  128,  131,  140,  142,  151. 

ingot  molds,  128,  154. 

ingots,  weight  of,  197. 

life,  137-38. 

lime  in,  56-57,  146,  148. 

lining,  57,  138-39,  140-41,  142- 
43,  146,  160. 

melting  platform,  127-28. 

molteh  pig  in,  127,  155-56. 

natural  gas  in,  167-68. 

oil  in,  169. 

operation  of,  56. 

plant,  127-31. 

ports,  135-36,  137. 

regenerators,    129,   132-35,  136, 
137,  138,  169. 

repairs,  139-40,  141,  142-43. 

reversals,  144. 


Open-hearth    reversing  valves,  129, 

144,  165,  166,  167. 
roof,  136,  137. 
scrap  used  in,  55,  145. 
size  of,  144-45. 
slag  pockets,  132,  134,  135. 
stationary,    56,    132,    134,    138, 

139-41. 

tap-hole,  139-40. 
temperature,  134-35,  144. 
tilting,    128,    131,    132,   140-41, 

142-44,  157,  160. 
valves,  165,  166,  167. 
Wellman  type,  142-44. 
working  platform,  127-28. 
Open-hearth  process,  the,  56,  127-72. 
acid,  chemistry  of,  152-55. 
loss,  152-54. 

practice,  152-55,  159-60. 
recarburizing,  59,  124-55,  129. 

See  also  Acid  steel, 
basic,  chemistry  of,  147-52. 
fluxes,  146.      ' 
loss,  150. 

practice,  145-52,  155-60. 
recarburizing,  129,  150-^52. 
removal  of  impurities,  147. 

See  also  Basic  steel, 
boil  in,  156. 
charging,  145-6. 

compared  with  Bessemer,  60-63. 
compared  with  electric,  444. 
Monell  process,  158-59. 
ore  used  in,  144,  145,  146,  148, 

149,  150,  154,  156-60. 
oxidation  in,  156. 
pig-and-ore  process,  145,  156. 
pig-and-scrap  process,  145. 
recarburizing,  59,  129. 
rephosphorization,  150. 
special  processes,  155-60. 
Talbot  process,  157-58. 
teeming,  131,  142,  145,  151,  154. 
slag,  138, 140, 141, 146, 147, 148- 
50,  152,  154,  155,  157,  158, 
159,  160. 

steel  distinguished  from  Bessem- 
er, 67,  287-88. 


INDEX 


503 


Open-hearth  steel  for  railroad  rails, 

61-63. 
in  U.  S.,  53. 

not  often  very  low  carbon,  149. 
strength  of,  326,  327. 
stock,  129-30,  150,  155-56. 
teeming  ladle,  128,  151,  131,  381. 
Open  pass,  200. 

Operation  of  regenerative  furnace,  56. 
Ore  boats,  20.     See  also  Blast  Fur- 
nace for  ores, 
handling    mechanism    at    blast 

furnace,  22. 

used  in  open  hearth,  55,  148. 
Organic  acids  and  corrosion,  435. 

chemistry,  474-75. 
Osmondite,  393. 
Osmond's  polish  attack,  453. 

theory  of  permanent  magnetism, 

330-32. 

Osmotic  pressure,  480. 
Otto  Hoffmann  coke  oven.     See  Re- 
tort coke  oven. 
Overheating  of  steel,  221, 234,  370-82, 

391. 

Overfilling  the  pass,  200. 
Oxidation  by  and  in  paints,  431-33. 
definition  of,  463,  464. 
of  steel  in  tempering,  387. 
in  cupola,  264.     See  Loss  in  cu- 
pola. 

in  puddling,  57-58. 
Oxide  of  iron.     See  Oxygen. 
Oxidized  coatings,  435.     See  Scale. 
Oxidizing  agents,  423,  432,  474. 
Oxidizing  effect  of  slags,  59. 
Oxygen,  chemistry  of,  459,  462-64. 
in  blast  furnace,  32. 
in  cast  iron,  174,  341. 
in  steel,  54,  59,  60,  63,  173,  174, 
287,  324,  327,  328,  415,  424, 
428,  429. 

Packing  for  malleable  castings,  357, 

362,  364. 

Paint,  422,  429-33. 
Painting,  quality  of,  428-29. 
wrought  iron,  64,  42.8. 


Paints,  kinds  of,  431-33. 
Pass  in  rolling,  194. 
Pass-over  mill,  195. 
Pasty  condition  in  freezing,  339. 
Pasty  stage  of  solidification  and  phos- 
phorus, 339,  345. 
Pattern  molding,  238-62. 
Patterns,  designs  of,  260-62. 
Pearlite,  312,  313,  317,  321,  371,  390, 

392-93,  394,  452-53. 
Pellets  in  Bessemer  slags,  117,  118, 

120. 

of  iron  in  foundry  practice,  278. 
Penknives,  tempering  of,  387. 
Per-,  prefix,  474. 
Perfect  combustion,  463. 
Permanent  molds,  253. 

set  defined,  484. 
-  Petroleum.     See  Oil. 
Phlogiston  theory,  462. 
Phosphide  of  iron,  316,  323,  453. 
Phosphorus,  chemistry  of,  478-79. 
eutectic,  321,  341,  453. 
in    basic    open-hearth    process, 
56-57,    146,    147-52,    159, 
481-82. 

in  blast  furnace,  38. 
in  electric  smelting,  439-40,  446, 
in  iron  and  steel,  61,  62,  66,  67. 
74, 146,  180-83,  323,  326-27, 
329,  330,  335,  338-39,  341, 
342,  344-45,  346,  348,  349, 
350,  352,  354,  366,  374. 
in  ores,  15,  61. 
in  puddling,  57,  78. 
Photo-micrographic  apparatus,  454- 

55. 
Physical  changes,  458-59. 

properties  of  metals,  483-87. 
Physics,  introductory  to  metallurgy, 

458-87. 

principles  of,  482-87. 
used  in  crucible  process,  90. 
Pickling,  229,  430-31,  433. 
Picric  acid  etching,  453. 
Pig  beds  of  blast  furnace,  42,  43. 
Pigging  up  in    basic   open    hearth, 
148. 


504 


INDEX 


Pig  iron,  4,  5,  7, 11, 12, 16,  42,  43,  289. 
See  also  Cast  iron. 

ladles,  40. 

Pigment  in  a  paint,  431-33. 
Pig-molding  machines,  41-42. 
Pigs,  42. 
"Pig-washing"     process,     or     Bell- 

Krupp,  67-68. 
Piling,  muck  bar,  58. 

wrought-iron  scrap,  428. 
Pinion  housing,  207. 
Pinions,  204,  206,  207. 
Pipe,  61,  65,  220,  224. 

fittings,  manufacture  of,  366. 
Pipes  in  iron  and  steel,  173,  176-79, 

253,  262,  278,  339-40. 
Pipe-welding  rolls,  222,  223. 
Pitch  as  a  pigment,  433. 
Pitting,  427,  428. 
Pittsburg,  as  an  iron  center,  12. 
Plant  forms,  composition  of,  460. 
Plates,  65,  196,  201. 
Platinite,  401. 
Pneumatic  hammers,  430. 
Polish  attack,  317,  392,  452-53. 
Polishing    for    metallography,    448, 

449-51. 

Porosity  of  cast  iron,  340,  347. 
Porter-Allen  engine,  210. 
Porter    bar    for  ingots    in    forging, 

192. 

Porter  governor,  210. 
Potassium  bichromate  and  corrosion, 

424. 
Pouring,  in  crucible  process,  92. 

metal  into  Bessemer  converter, 

104. 
Power,  from  blast-furnace  gas,  30. 

consumed  in  rolling,  202,  203. 
Precipitation,  481. 

Preparation,  of  samples  for  metallog- 
raphy, 449-51,  452-59. 

of  surfaces  for  coating,  249,  430. 
Preservative    coatings.     See    Paint, 

Galvanizing,  etc. 
Presser  board,  258. 
Pressing,  227-29. 
Pressing  linseed,  432. 


Pressure  on  steel,  methods  of  apply- 
ing, 187. 

and  volume  of  gases,  482. 
Price  of  Bessemer  pig  iron,  61. 
Priming  coat,  429,  232. 
Process.      See    Index    to  authorities 

cited. 

Producer-gas,  160-72. 
Production  of  steel  in  U.  S.,  65. 
Projectiles,  386. 

Properties  of  cast  iron,  the,  345-55. 
Puddle  balls,  58. 
Puddled  bar,  58,  83. 
Puddle  rolls,  58,  82. 
Puddling  furnace,  57,  74-94. 

process,  57-58,  74-94. 

slag  or  cinder,  57. 
Pulling  in  crucible  process,  91-92. 
Pull-over  mill,  195. 
Purification  of  pig  iron,  51-72. 

Qualitative  chemistry,  461. 
Quantitative  chemistry,  461. 
Quarternary  steels,  397,  407-13,  415- 

16,  418. 
Quartz,  476. 
Quenching    steel.        See     Hardening 

steel. 

Rabbling  in  air  furnace,  360. 
of  puddling  process,  78,  79. 

Radicals,  471-74. 

Ragging.     See  Roughing. 

Railroad  car  wheels.     See  Car  wheels. 

Railroad  rails,  61-63,  65,  194,  196, 
215,  219-21,  328-29,  330, 
400,  406,  456. 

Rammers,  molders',  242. 

Ramming  molds,  241-43,  246. 

Rapping  patterns,  240,  252,  258-59. 

Rate  of  cooling,  effect  on  iron,  308, 

336,  345,  356. 
cooling  of  steel,  382-95. 

Razors,  forging  of,  192. 

Recarburizing,  397, 415, 437.  See  also 
Bessemer  Process;  Open- 
hearth  process. 

Recuperative  heating  furnaces,  230, 
231,  232. 


INDEX 


505 


Red  lead,  432. 

Red-shortness  of  cast  iron  and  sul- 
phur, 341. 
of  steel,  326. 

Reducing  agents,  474,  475,  496. 

Reduction,  definition  of,  463,  464. 
of  area  defined,  484-85. 

of  steel  under  strain,  186. 
of  metals  in  rolls,  194,  193-235, 
220. 

Reel,  226. 

Refinery  hearth,  68. 

Refining  steel,  371.  See  also  Crys- 
tallization. 

Refractory  clays,  477. 

Regenerative  furnace.     See  also  Cru- 
cible process;    Open-hearth 
furnace, 
heating  furnaces,  231. 

Repairs  for  steel-casting  furnaces,  287. 

Repeated  stresses,  398,  416,  485. 

Rephosphorization  of  steel,  59-60. 
See  Open  hearth. 

Rerolling  rails,  220. 

Residual  silicon  in  Bessemer  process, 
112. 

Resilience,  399,  484,  486. 

of  malleable  cast  iron,  356,  366. 

Restoring  steel,  371,  380,  388-89.  See 
also  Crystallization. 

Retort  coke  oven,  13,  14,  15. 

Return  scrap,  367. 

Reverberatory  furnaces,  for  heating, 
229-31. 

Reversing  mills,  197,  198,  199,  204, 
208,  209,  210,  211,  212,  219- 
20. 

Risers  on  castings,  177,  182, 189, 241, 
253,  262,  349. 

Rivets,  402,  485. 

Roberts-Austen,  Roozeboom  dia- 
gram, 312,  314-15. 

Rock  drills,  tempering  of,  387. 

Rock-over  molding  machine,  255. 

Rod  mill,  203. 

Rods,  wire.     See  Wire  rods. 

Roe  puddling  furnace,  76-77,  83-84. 

Rolled  steel,  crystallization  of,  381. 


Roll  engines,  205,  211,  212,  217,  210- 

12. 

Roller  table  engine,  204,  208,  212. 
Rolling,  193-235. 

compared  with  hammering,  193. 
effect  of,  193-95,  375-78,  381. 
mills,  203-15. 
delays  in,  206. 
parts  of,  200-25. 
speed  of,  194,  196. 
Roll  scale  used  for  fettling,  75. 

chilled,  337,  352,  419. 
Rolls,  200-3. 
Roll  tables,  206,  208,  209,  212,  213, 

214,  217,  218,  221. 
Roozeboom  diagram,  312,  314-15. 
Rosin  in  paint  vehicles,  432. 
Rotary  squeezer,  76. 
Rouge  for  polishing,  preparation  of, 

450. 

Roughing  of  rolls,  201,  202,  203. 
Rule  cf  smelting  and  oxidation,  52. 
Running-out  fire,  68. 
Rust,  422-24,  458,  459,  460. 
Rusting  of  iron  and  steel.     See  also 
Corrosion. 

Saggers,  362. 

Salt  used  in  rolling,  217. 

Salts,  472. 

Sand  blast,  362,  430. 

in  rolling,  217. 

for  molding,  243. 
Sand-casting  of  pig  iron,  42. 
Sappy.     See  Silky. 
Saturated  martensite,  392. 
Sault  Ste.  Marie,  20,  21. 
Sauveur  method  of  etching,  453. 
Saws.     See  Wood  saws;  Hacksaws. 
Scabs  on  castings,  243. 
Scaffolding  of  blast  furnace,  44. 
Scale,  219,  231-35,  425,  428,  429. 
Scaled  castings,  366. 
Science  in  the  iron  foundry,  236. 
Scintillating  of  steel,  379. 
Scrap,  analysis    of,    274,    275,  278, 

285. 
Scrap  iron,  grain  of,  278. 


506 


INDEX 


Scrap  produced  in  forging  cannon, 
192-93. 

used  in  iron  castings,  53,  275, 
278,  285,  354,  366-67. 

used  in  steel  manufacture,  53, 

90,  105. 
Screw-down    mechanism,   206,   208, 

209,  217. 

Sea  water  and  corrosion,  426-27,  431. 
Seamless  tubes,  making  of,  222—24. 
Second-class  rails,  220. 
Segregate,  180-83,  193. 
Segregation,  '  173,  180-83,  341,  348- 
49,  350,  402,  415,  424,  427- 
28,  456. 
Selective  freezing,  304. 

precipitation,  300,  309,  311. 
Self-fluxing  in  blast  furnace,  47. 
Self-hardening  steels,  408-11. 
Semi-steel  castings,  368. 
Sesqui-oxide  of  iron,  474. 
Sesqui silicate,  477. 
Shape  produced  by  rolling,  194,  197. 
Shearing  strength,  485. 
Shear  steel,  87. 
Shears,  218. 
Sheets,  65. 

Sheffield,  England,  15,70,86,87,88. 
Shingling,  77. 
Shock,  485. 

Shop  vs.  fieH  painting,  430. 
Shovel  loading  soft  ore,  18. 
Shrinkage,  482. 

cavity.     See  Pipe. 

of  cast  iron.     See  Cast  iron. 
Shrinking  of  molds  in  drying,  246. 

outer  cannon  tubes,  193. 
Siderite,  15. 

Silica,  476,  478-79,  482. 
Silica  wash,  245. 
Silicates,  476-77. 
Silicide  of  iron,  316,  324. 
Silicon,  chemistry  of,  476. 

control  of  in  pig  iron,  35-38,  45, 
342. 

in  air  furnace,  284. 

in  basic  open-hearth  process,  57, 
146,  287. 


Silicon,  in  Bessemer  process,  60,  95, 

110-12,  114-15. 

in  cast  iron,  308, 329, 335, 341-43, 
345,  346,  347,  349,  350,  351, 
352,  354-55,  481. 
in  crucible  process,  91. 
in  malleable  cast  iron,  356,  360, 

365,  367. 

steel,  54,  66-67,  174,   182,  274, 
326,  330,  396.     See  also  Sili- 
con in  cast  iron, 
steel,  330,  396,  413-14. 
Silico-Spiegel,  analysis  of,  104. 
Silky  fracture,  370,  380. 
Silver-gold.     See  Gold-silver. 
Single-shear  heat,  87. 

steel,  87. 
Size  of  castings  and  shrinkage,  346. 

of  crystals.     See  Crystallization. 
Skelp,  65,  221. 

Skimmer  of  blast  furnace,  40. 
Skimming  the  air  furnace,  360. 
Skin-dried  molds,  245. 
Slabbing  mill,  200,  203,  212,  217. 
Slabs,  217,  234. 
Slacking  of  lime,  479. 
Slag.     See  also  Cinder. 
Slag  and  corrosion,  425,  425-28. 

distinction     under     microscope, 

452. 

in  steel,  66. 
in  wrought  iron,  4,  58,  64,  66,  77, 

81,  83,  85,  317. 

made  in  heating  furnaces,  233. 
Slags,  419,  439-40,  463,  474,  476,  477, 

478,  479,  481. 
Slick  for  molding,  242,  245. 
Slip  bands,  186,  399. 
Slips  in  blast  furnace,  44. 
Smelting  in  U.  S.,  distribution  of,  16. 
Law  of.     See  Law  of  smelting, 
zone  of  blast  furnace,  30. 
Smoke,  producing  rust,  43,  431,  432. 
Soaking  pits,  111,  231-33. 
Solidification,  177,  338,  339,  341.    See 

also  Freezing. 

Solid  solutions,  292-95,  304-15,  345, 
385,  389-95,  402,  411. 


INDEX 


507 


Solubility,  480. 

Solute,  480. 

Solutions,  292,    293,   292-315,    479- 

82. 

Soo  canal.     See  Sault  Ste.  Marie. 
Sorbite,  325,  389-95. 
Soundness,  246,  326,  400. 
Sows,  42. 

Spanish  ore  used  in  U.  S.,  17. 
Spathic  iron  ore,  15. 
Specific  gravity,  482. 
Spectroscope    in    Bessemer    process, 

105. 

Speed  of  cooling.     See  Rate  of  cool- 
ing, 

Spiegeleisen,  103,  104,  105. 
Spike  rods,  65. 
Spindles,  204-12. 
Spitting    in    Bessemer   process,    95," 

290. 

Splice  bars,  65. 
Spongy  spots  in  cast  iron.     See  Cast 

iron. 

Spring  heat,  87. 
Springiness.     See  Resilience. 
Springs,  tempering  of,  387. 
Sprues,  252,  259. 
Squeezers,  76,  258. 
Stack  of  blast  furnace,  24. 

of  cupola,   264,   268,  272,  273, 

279-84. 

Stead's  brittleness,  381-82. 
Steam  hammers,  187-93,  227-28,  229, 

compared    with    electric    motor 

drives  for  rolls,  213. 
Steel  castings,  247,  356. 

compared  with  white  cast  iron, 

226. 

Steel-conversion  process,  85-87. 
Steel-converting  furnace,  86. 

definition  of,  7. 

description  of,  4. 

in  wrought-iron  piles,  428. 

ladles,  106. 

pipe  made,  224. 

production  of  different  countries. 
63. 

rolls,  201. 


Steel,  strength  of,  67,  185,  189,  224, 

324-29,  350,  371,  392. 
through  heat,  87. 
uses  of,  65. 
vs,  cast  iron,  333. 
Stiffeners  on  rolls,  200. 
Stone-cutting    tools,    tempering    of, 

387. 

Stools  for  ingot  molds,  107-8. 
Stoppers  of  steel  ladles,  106. 
Stoughton  converters,  289-90. 
Stove  foundries,  use  of  scrap  in,  278. 
Stoves,  blast  furnace,  2,  27,  28. 
Straightening  rolls,  218. 
Strain  defined,  483. 
Strain,  effect  of,  on  steel,  186. 
Strength  of  welded  pieces,  378. 
Stress  defined,  483. 
Stripping  ingots,  108-9. 
Stripping-plate    molding    machines, 

253-258. 
Strips,  65. 

Structural  shapes,  rolling  of,  196. 
Structure  of  eutectics.     See  Eutec- 

tics. 

Sub-,  prefix,  474. 
Subsilicate,  477. 
Sulphate  of  lead  or  zinc  as  pigments, 

432. 
Sulphide  of  iron,  316, 322-23, 343, 349, 

473. 
of  manganese.     See  Manganese 

sulphide. 

Sulphur,  chemistry  of,  478. 
Sulphur  elimination  in  mixer,  98. 
Sulphuric  acid,  430,  433,  478. 
Sulphur  in  air  furnace,  284. 
in  blast  furnace,  34,  36. 
in  cast  iron,  180-83, 308,  323-23, 
335,  341,  342,  343^4,  346, 
348,  349,  350,  352,  354-55, 
365-66,  374. 

in  electric  smelting,  439-40,  446. 
in  puddling  process,  78. 
in  steel,  67, 308,  322-23, 326, 374. 
See  also  Sulphur  in  cast  iron. 
Sulphurous  acid,  478. 
Surface  tension,  480. 


508 


INDEX 


Surgical  instruments,  tempering  of, 

387. 
Sweden,  recarburizing  Bessemer  in, 

120. 

Swedish  iron,  317,  330,  446.    See  Nor- 
way iron. 

Swedish  Lancashire  process,  70-72. 
Sweeping  a  mold,  236-37,  255. 
Swelling  of  a  casting,  243. 
Swords,  tempering  of,  387. 
Synthesis,  461,  464. 

\ 
Table,  engines,  215. 

roller,  205,  208,  209,  212. 
Talbot  process,  157-58. 
Tap  cinder,  85. 

Tap-hole  of  cupola,  266,  267,  280-82. 
Tappings,  85. 
Tar  as  a  paint,  433. 
Taylor    revolving    bottom    gas-pro- 
ducer, 161. 

Teeming  steel  into  molds,  106-7. 
Temper,  carbon,  357,  358,  365,  367. 

colors,  387. 
Temperature,  and  affinity,  460. 

and  volume  of  gases,  482. 

annealing  malleable  castings,  357, 
364. 

blast  furnace,  336. 

casting,  60-61,  287,  346,  354. 

defined,  465. 

drying  ovens,  243. 

effect  on  solubility,  481. 

expanding  cannon  tubes,  193. 

hardening  steel,  382. 

welding,  377. 
Temperatures,  annealing,  388-89. 

Bessemer  process,  53,  105, 106-7, 
116-17. 

electric  smelting,  437. 

finishing  in  rolling  and  hammer- 
ing, 190,  229,  375-78. 

finishing  in  welding,  378. 

open-hearth  furnace,  134-35, 144. 

to  produce  ingotism,  381. 

to   produce   Stead's   britcleness, 
381,  382. 

puddling,  83. 


Temperatures,   restoring  steel.     See 
Crystallization;  Restoring. 

rolling,  196,  203,  217,  234,  374, 
375. 

tempering,  386-87. 
Tempered  steel,  constituents  of,  389- 

95. 
Tempering,  412-13. 

fire  clay  crucibles,  90. 

of  steel,  386-95. 
Tenderness    produced    by   ingotism, 

197. 

Tensile  strength,  defined,  483. 
Ternary  alloys,  396-97. 
Terne  plate,  435. 
Texture  of  center  of  ingots,  193,  228. 

See  also  Ingots. 
Thermo-chemistry,  464-66. 
Thermo-electric    power,     385,     387, 

394. 

Third-class  rails,  220. 
Third  rails,  330. 
Three-high  mill,    195,   195-97,   200, 

206-7,  219. 

Throat  of  blast  furnace,  24. 
Three-ply  plate,  195. 
Tie-rods  for  furnaces,  381. 
Tilting,  189. 
Time,  in  air-furnace  operation,  285. 

in  open  hearth,  55. 

of  drying  molds,  243. 
Tin,  430. 

lead.     See  Lead-tin. 

plate,  61,  195,  422,  435. 
Titanium,  15,  419,  396. 
Tool  steels,  408-13. 
Torsion,  485. 
Total  carbon  in  cast  iron,  336,  344, 

348,  350,  358,  366-67. 
Toughness,  defined,  486. 
Transfer  tables,  210. 
Transportation  of  iron  ore  in  United 

States,  16,  17,  20. 
Transverse  strength,  350,  352,  485. 
Tri-,  prefix,  473. 
Trisilicate,  477. 
Tri-valent,  473. 
Troostite,  389-95. 


INDEX 


509 


Tropenas  converters,  288-89,  290. 

Troubles  in  rolling,  215. 

Trowels  for  molding,  242. 

Tubes,  drawing  of,  226. 

Tubing,  lap-welded,  221-22. 

Tumbling  barrel,  362. 

Tungsten,    effect   on   crystallization, 

374. 

Tungsten  steel,  397,  396,  408-13. 
Tuyere  notches,  24. 
Tuyeres,  of  Bessemer  converter,  98— 

99,  100-2. 

of  blast  furnace,  24,  25. 
Two-high  mill,  200,  206,  219-20. 

Uehling  pig-casting  machine,  41. 
United  States  iron  ores,  16,  17. 
Uni-valent,  473. 
Universal  mill,   197,   199,  208,  209, 

212,  216. 

Unloading  ore  boats,  20,  21. 
Uses  of  pig  iron,  51. 

Valence,  472-73. 

Vanadium  steel,  396,  414-19. 

Vehicle  of  paints,  431-33. 

Venting  molds,  240,  249. 

Vertical  rolls.     See  Universal  mill. 

Vibration  and  crystallization  of  steel, 

374. 

Vibrator  molding  machines,  256-59. 
Vibratory  stresses  in  steel,  327. 
Volume  of  gases,  482. 

Walloon  charcoal  hearth,  70-72. 
"Washed  metal,"  produced  by  Bell- 

Krupp,  68. 

Washes  for  molds,  240,  243,  243-46. 
Waste.     See  also  Loss. 

gas  from  blast  furnace,  27. 
Water,  composition  of,  460. 

cracks  in  steel,  386. 

gas,  170-72,  469. 

gas-producer,  171. 

gates,  262. 

on  rolls,  217. 

-sealed  gas-producers,  162-63. 

-sealed  reversing  valve,  166,  167. 


Weather  loosening  scale,  429-30. 
Weight,  and  volume  of  air  compared, 

27. 

Welded  pipe,  61. 

Welding,  64,  195,  377-78,  415,  428. 
Weldless  tubes,  222-23. 
Wet  chemistry,  475. 
White  lead  as  pigment,  432. 
Whitworth's  liquid  compression,  179. 
Wind  in  cupola.     See  Blast  pressure. 
Wire,  61,  224-26,  328. 

brushes  for  cleaning  steel,  430. 

rod  frame,  225. 

rod  rolling  train,  225. 

rods,  65,  196. 
Wobblers,  203,  205,  206. 
Wood  saws,  tempering  of,  387. 
Wrought  iron,  as  malleable  iron,  369. 

compared  with  knobbled  iron,  70. 

compared  with  low-carbon  steel, 
64. 

corrosion  of,  vs.  steel,  425-29. 

crystallization  of,  381. 

definition  of,  7. 

description  of,  4. 

distinguish  from  steel,  66. 

electric  conductivity  of,  329. 

ferrite  in,  317. 

from  scrap,  428. 

heat  treatment  of,  381. 

in  United  States,  53. 

manufacture  of,  74-94. 

modulus  of  elasticity  of,  484. 

not  hardened  by  quenching,  195. 

pipe  made,  224. 

properties  of,  64. 

scrap  used  in  United  States,  53. 

slip  bands  in,  186. 

strain  test  of,  65. 

tensile  strength  of,  65,  483. 

uses  of,  51-52,  65, 64, 90, 317, 330. 

Zinc,  430.     See  also  Galvanizing. 

melting  point  of,  434. 

salts  as  pigments,  432. 
Zone  of  combustion  in  cupola.    See 

Tuyere  zone. 
Zones  of  cupola,  264-85. 


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